Yes, it's quite easy to install and wipe a whole hard drive and have a pure Linux system. When all my friends and coworkers were lusting after Vista, I decided to throw out all my Windows garbage and start with a fresh computer. Thus far, EVERYTHING has been better and faster. And I used to be a Windows software developer, so we're talking LOTS of software. Absolutely NO regrets!
Some distributions allow you to run from a "Live CD" so that you can check it out before installing. I've actually run and installed several, and here are my findings thus far:
Debian: Most likely to run on older machines. The "grand daddy" of many other distributions. There is no Live CD option for this one. If you're on a high-speed, you might want to try the Network Install CD. Downloading the full-blown version might take a while... it's a massive 14-CD set. Uses the Gnome desktop.
Ubuntu: Outstanding support. They'll even send you the CD for free if you're on a slow connection and/or can't burn it yourself.
Kubuntu: This is Ubuntu, with the KDE desktop instead of Ubuntu's default, Gnome. In a nutshell, Gnome gives you a sort of "Mac" look-and-feel, and KDE behaves more like Windows. That's an over-simplification though. Some programs are designed specifically for Gnome or KDE, but many these days will run with both. Plus, no matter which desktop is your favorite, you can always install BOTH and pick one before you log into your system.
Mandriva 2007: This has both a one-CD live install version and a 4-CD set for a full hard drive install. You'll need file-sharing software to download (BitTorrent, Limewire, etc) as it's only available as a torrent. This is the version I'm running right now, as it's the only one thus far that was able to recognize my ancient SoundBlaster 16 (ISA) without a lot of tweaking. The live single-CD comes in both Gnome and KDE editions. The 4-CD set lets you choose from several desktop options.
Knoppix: This one is really designed to be run ONLY as a live-CD, but you can also have it copy it's CD images to the hard drive during the boot process, freeing up your drive. If you can burn a DVD on your system, download that version and you'll have everything but the kitchen sink. A full-blown office suite (SunSoft's OpenOffice). Graphics software that should make Adobe blush (Gimp). Burning software that makes Nero look like a toy (K3B). The advantage here is that when you combine the bootable CD/DVD with a USB jump drive, you can have your whole system with you where-ever there's a computer. Plus it's handy for doing troubleshooting if things start to go wrong with your hard drive. This one is KDE-based.
Final thoughts: For ease of use and support, my vote goes for Ubuntu/Kubuntu. Ubunto (Gnome) looks a bit cleaner to me, but Kubuntu (KDE) has some slick features built-in that I missed in Gnome.
The only possible reservation is that Ubuntu departs from standard Linux in that there is no "superuser" (root). Instead you have to supply your password at inopportune moments, and when you're running from a command line and need super-user access, you have to use a utility called "sudo" instead. This can cause a bit of a challenge with some programs that expect to be run first as the superuser during the install process.