You didn't indicate if your ISP is broadband cable or broadband DSL. Mac OS X has built-in features that allow users to connect to a DSL Internet broadband service, using an assigned PPPoE login name and password for authentication.
1.Click on the Apple Menu icon on the Desktop menu bar.
2.Select System Preferences.
3.In the System Preferences window, click on the Network icon.
4.In the Network window, click on the selection arrows for the “Show” drop-down menu and choose Built-in Ethernet or Airport (depending on which connection method is being used).
5.Click on the PPPoE tab.
6.Check Connect using PPPoE.
7.Click on the Apply Now button to save your changes.
If you have a router, this option should be unchecked, then configure the router for PPPoE.
For Cable broadband, the ISP normally gives you a software plus they may need to register your MAC Address (I believe its called an ethernet ID or address for mac OS).
For the second question... sorry, I'm not familiar with Mac OS settings when it comes to file sharing.
Okay, knowing how frustrating this can be hope the following helps:
The Mac that will be doing the sharing:
1.Choose System Preferences either from the Dock or from the Apple Menu.
2. Select the "File Sharing" icon, under the "Internet and Network" catagory.
3.Turn on File Sharing.
The Mac that will connect to the file sharing Mac
1.In the Finder, select "Connect to Server..." from the Go menu.
2.From the list that appears, navigate your way to your file sharing Mac's name, and click Connect.
3.Enter your user name and password that you use when you log in normally on the Mac that is File Sharing. If the Mac your connecting to is running OS 9, then the user name and password will be the ones that you have set in the File Sharing Control Panel.
4.The File Sharing Mac's hard drive icon will appear on your desktop. Congradulations, you're sharing! You can copy to or from your files on that Mac.
5.Be sure you drag the icon of the File Shared Mac to the Trash (in the Dock) when you're done. This will log you off that computer.
http://wcts.whitman.edu/whit.bits/october2002/MacintoshFileSharing/FileSharingOSX.html
Here's another Article-
http://helpdesk.wisc.edu/page.php?id=256
Assign yourself a username and password
In order to allow you to access your files remotely, you will need to give yourself a username and password which will let you log in to your computer from another Macintosh. Open the File Sharing control panel (or Sharing Setup control panel on older versions of Mac OS), which is under Control Panels under the Apple menu.
In the Owner Name field, type the name that you would like to use as your username. If you wish, it can be the same as your e-mail username. Then, type a password of your choice into the Password field. This can also be the same as your e-mail password, but remember: no matter what you pick, be sure to keep your password secure. If someone knows your password, they could connect to your computer and access your files. In the Computer Name field (or Macintosh Name field on older versions of Mac OS), type in a name for your computer. It can be anything you like, but should be something that allows you to easily identify your own computer.
Once you have completed the above steps, click on the Start button in the File Sharing section of the window, directly below where you entered your username and password. You do not need to start Program Linking.
Check that your Macintosh is set up to use the network
File sharing uses a special communcation protocol called AppleTalk. This is different from the type of communication that occurs when you use the web or e-mail. Open the AppleTalk control panel, which is under Control Panels under the Apple () menu. Make sure Connect via is set to Ethernet. Your AppleTalk control panel should look something like this, though Current zone will be different depending on which building or residence hall you are in:
Important: remember the zone name next to Current zone in your AppleTalk control panel. You'll need to know this to connect to your Macintosh.
Make sure your Macintosh doesn't go to "sleep"
Newer Macintosh computers have a feature which lets them go to "sleep" after a period of inactivity, usually 30 minutes, to save energy. Unfortunately, you won't be able to access your Macintosh remotely if it has gone to sleep. To make sure your computer doesn't go to sleep, open the Energy Saver control panel, which is under Control Panels under the Apple () menu. Move the sleep control slider to the "Never" setting:
At this setting, your screen will still dim, but the computer will stay awake so that you can connect to it remotely. If you don't have an Energy Saver control panel, your Macintosh most likely is a model which doesn't sleep.
That's it! Now you're ready to connect to your Macintosh computer from any other Macintosh on the UW campus network.
Connecting to your Macintosh from another Macintosh
In order to connect to your computer from other places on campus, you'll need to leave your computer turned on, or make sure someone will be there to turn it on for you when you need it. The Macintosh you use to connect to your computer must also be directly connected to the network via ethernet. Good examples of these would be Macintoshes in University office buildings, the InfoLabs, or on ResNet. Let's imagine that you'd like to access your computer from a Macintosh in the InfoLab at Memorial Library, and your computer is on ResNet in Witte Hall. You can sit down any Mac at the Memorial InfoLab. To access your computer, select the Chooser from the Apple () menu.
In the Chooser, click on the AppleShare icon on the left. In the AppleTalk Zones section, find the zone that your Macintosh is in and select it (this was in the AppleTalk control panel of your Macintosh). If your Mac is on ResNet, the zone name is usually RESNET, followed by a dash and the name of your residence hall. On the right side of the Chooser, your Macintosh name will show up. Select your Macintosh, and press OK.
Type in your username and password, and press Connect. A window will appear that lists the name(s) of the hard drive(s) on your Macintosh.
Select the your hard drive, and press OK. You may now close the Chooser. On the desktop, below the normal hard disk icon, an icon representing your hard drive will appear.
When you open it, you will find it contains all the files that you are familiar with seeing on your own Macintosh. You can copy, move, edit, and print any of your documents, such as a word processing file; you can check your e-mail using the settings on your own computer without using a disk; you run programs that are only on your own computer; you can copy a document you may have been working on at the InfoLab to your own computer, or vice versa. When you connect to your computer using file sharing, you have access to all the files you would normally have if you sat right down in front of your computer.
Once you are done using your computer, close all the documents that reside on it and quit any programs you may have been using. Then, drag the icon on the desktop representing your hard drive to the Trash. This doesn't delete any files; rather, it disconnects you from your computer. Make sure to disconnect yourself when you are finished, or the next person to sit down at that computer would have access to your computer and all your files. As long as you remember to disconnect, and you keep your password secure, no one but you will be able to connect to your computer.