CompUSA sucks! Be careful!
If you can create a boot disk you might be able to boot off a floppy and point to where XP is on your drive which get you back up.
Or try a Windows XP CDROM with the recovery option. I doubt that your data is lost. Most likely you just have a problem with your system files or master boot record MBR.
Check this out:
http://www.bootdisk.com/bootdisk.htm
You may need to edit the boot.ini on your floppy to tell XP where to find it on your drive.
[boot loader]
timeout=05
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
C:\CMDCONS\BOOTSECT.DAT="Microsoft Windows Recovery Console" /cmdcons
Hope this helps!
Mike
Nice to see someone with a grasp of the problem and not someone who just wants to up their post count by creating more problems... :)