Yes it is possible to run both IDE and SATA. However, what you want to do is you want to make one or the other your primary hard disk and keep the other hard disk(s) off line until you install Windows.
Windows natively wants to install to an IDE drive. This is because IDE was the de facto standard for 20 years. Now, SATA has taken over. What I am saying is, Windows can get confused if you have both types of drives connnected to the computer when you install Windows. Especially, if you have a SATA drive you want to make the primary drive and the old IDE a secondary drive. This can throw windows for a loop. The other problem is that you will need to load the uncompressed drivers for SATA during Windows installation for Windows to detect a SATA drive. Here is what you will want to do to avoid problems:
1). From the new motherboard CD, locate the SATA drivers. On ASUS motherboards, you can do this at the DOS level on boot, by having the CD drive as primary boot device, have the motherboard cd in the drive on bootup and have a formatted foppy disk available. Asus will start up the SATA decompression utiity and will give you a menu choice to write the uncompressed drivers to a floppy disk(s). Since you have a Gigabyte CD, check your mobo manual to find out how to locate and uncompress the SATA drivers from the CD or see if they offer a decompression utility at the DOS level.
Either way, decompress the SATA drivers to a temporary directory on your hard disk. Then, if you do not have a floppy drive, write the uncompressed drivers to a CD disk (using DATA CD as the type of disk). You now have a driver CD with the uncompressed SATA drivers.
Initially, only have the SATA drive (plugged into SATA1 port on the motherboard) connected to the electrical connector from the psu. You can have the old IDE drive in place, with the IDE ribbon connected, just do NOT connect the electrical molex connector yet. Therefore, Windows installer will NOT detected the IDE drive during installation.
Proceed to start the Windows installer. Hold down F6 in the beginning to let Windows installer know that you wish to load proprietary drivers. Windows will load stock generic drivers and then ask you for the proprietary drivers (both XP and Vista do this). At the request, take your Windows disk out of the drive and insert your SATA driver CD in the drive and load all the drivers from the CD into Windows installer. Once the drivers are loaded, put your Windows CD back in the CD or DVD drive. Proceed as normal with the install...
Windows then detects your SATA drive, you can then format, partition and install Windows.
Once Windows is installed on the SATA drive and is up and running, then shut the computer down. Connect the molex connector to your IDE drive, configured as PRIMARY on the IDE port (Master device). Boot back up and Windows will detect the IDE drive and you will be up and running with both kinds of drives.
If you have a SATA CD/DVD drive, you would connect it to SATA2 on the motherboard, no jumpers required.
If you have an IDE CD/DVD drive, set the drive with the jumper in back to SLAVE on the IDE port.
This outta do 'er.