one word answer...... yes.
more elaborate answer: Yes.
can't really elaborate on that actually. lol. when you install XP, you're installing it on one partition. Hence, if you have two partitions, with one set for backups (be it drivers/apps you can install post-format, or an actual backup to restore (but since you asked if your backups would be safe after reinstalling XP, i'm assuming not the latter)) and you format and install on the same partition XP is on now, you will only be doing stuff with that partition. all others will be safe.
i've done what you are thinking for quite some time now, keeping my drivers, anime, music, etc... on one partition, and installed XP on another. even most retail PC manufacturers now tossed backup CD's for a backup partition on the hard drive.
hell...... at one point i even transferred stuff to my laptop to save it. my laptop basically turned into a removable backup storage that i could view what was backed up on. lol
i even use my Gmini402 20GB MP3 player as removable storage/backup.