↑↑ that's all very nice, but the question is about windowsXP, not windows7 and windowsXP can not be installed from a flash drive using that method.
For re-installation purposes it really would be easiest just to get a USB DVD drive like the one in Mark's link up there ↑↑↑
If you really don't want to spend the £25 odd quid on a DVD drive it is possible to make a bootable USB stick to install XP from, but it's not a matter of just copying the files to the USB stick.
http://www.ocia.net/a...lashdrive/page1.shtml