Boot from the XP cd. When the setup screen appears, press R to enter the Recovery Console, then press 1 and hit enter (when asked which xp installation), enter your password and press enter, now you should be at the command prompt. Navigate to the folders where your pictures are stored and copy them to the flash drive.
If you dont have the XP cd, you can use a bootable cd/dvd like UBCD or Hiren's. I often use Knoppix in such situations. Knoppix is a live CD linux distro, ideal for this kind of jobs. You'll need to download it and burn to CD.