If the flash drive is big enough maybe more of a 16 or 32 G size -

- or if you limit only files & settings and not the whole windows system files
- or if the flash drive has a built in compression program.

most will tell you at some point of the process of backing up - if it runs out of room. But then you have to go re select fewer files to back up. and start over.

Here are some easy back up programs that might be very helpful & much easier than the windows backup utility ( it has to be installed from the Windows CD -XP anyway)

read about them -and the comments on the bottom of the page for each program - before trying it.
If you try one and don't care for it - uninstall it & just try a different one sometime I try 3-4 before I find one I like.

http://download.cnet.com/EaseUS-Todo...-10964460.html

http://download.cnet.com/Cobian-Back...-10071828.html

http://download.cnet.com/GFI-Backup-...-10915610.html