Sorry, scratch what I was gonna say... this guy on another forum put it SOOOO much better than I could! I'll copy and paste!
Similar problems are usually caused by a incompatible or unsupported (At least out of the box) disk controller. If your friend's system uses a SCSI, RAID or UDMA disk controller instead of the regular IDE channels, then this could be your problem.
You may also want to make sure "BIOS shadowing" and "virus protection" are turned off in your BIOS if such options exist.
If you think your friend may have an integrated UDMA controller, but aren't sure, you will probably notice on bootup that the hard drive(s) are not listed in the initial post of the BIOS screen. Instead, they may appear later on a seperate screen. Disk controllers have their own "BIOS" and work independantly of the motherboard.
If that doesn't make sense (I'm not very good at explaining things sometimes), then find out from your manufacturer's website or your motherboard manual on whether you or not you have a seperate UDMA disk controller.
If do have a integrated/internal disk controller, then you will need to get the most recent Windows XP drivers for it. You can usually do this at your computer manufacturer's website (store-bought PC) or the manufacturer of the disk controller's website (homemade PC).
What you will need to do is download the newest controller drivers for Windows XP.. Then place the drivers on a floppy disk. (Do not place the files in a folder on the floppy disk (Bad Example - A:\drivers\driver.cat). You will want to make sure all the files are accessible on the root of A:\ (Good example: A:\driver.cat).
When you try to install Windows XP again, near the beginning of the blue pre-installation process, you'll see a message that pops up that says something like this, "To install third party SCSI or RAID devices, press F6". You will want to press F6 here and wait a minute or two for it to do its thing.
Pop in your floppy disk when it asks for it and follow the steps it gives you. "s" specifiies a device and "Enter" basically says, "Okay". You'll need to specify two devices (usualy) since there are often two UDMA controller channels... Then continue with the installation as usual. It should work.....
If you don't have a special disk controller, then ignore all that.