Insert a blank floppy into you floppy drive, right click on your floppy drive and select format. When the format box comes up, click the pull down menu and select boot disk.
You're using XP? Do you have the XP CD? Windows 2000 and XP are configured by deafult to boot off the CD.
So just insert the CD and restart. The Windows XP setup is mega easy. All you have to do is select a harddrive or partition to install Windows on, select which type of formatting you want and boom!