All WinXP applets stopped working

[gf4200isdabest]

i was installing some updates from my college's deployment site; while Office SP1 was going, i tried downloading the Ad-Aware SE PRO install...it gave me an error about 2 going at once so I waited for office to finish, tried again, nothing happened...decided to restart. Now whenever i attempt to launch anything part of the windows system it won't work. The OS starts, applications such as wordpad, firefox, etc run just fine; however, i can't access task manager, regedit, mspaint, add/remove programs, etc. Essentially, anything that's an applet of explorer won't run. I suspect either SP1 or the ad-aware install that wouldn't go to be the culprit. however, since i can't actually uninstall programs with the windows app I'm stuck. I'm sure a reinstall of the OS would fix it but I'd rather not go this route for now. I doubt it's a virus, Avast Pro is always running and was updated earlier today.