He didn't say that he was trying to boot from floppy, sounded like he wants to boot a hard drive that already has XP installed. Check the boot order in the BIOS...if it's an Award BIOS you probably...

I would try plugging it in and see if Windows picks it up, if it can read the partition it will put it as a secondary drive for you...if not you might try booting from 2K/XP cd and format it.