There is a very simple solution to this problem.
Insert your XP CD into the drive, and reboot. When prompted to boot to CD, slect yes. When windows Setup is finished loading, press Enter to continue installing Windows. Agree to the TOU, and then, instead of Pressing ESC to remove your old install of Windows and install a new copy, press R to repair a previous install. Windows will reinstall all core components, core OS files, and basically put a fresh install of XP on your machine. It won't, however, remove any programs, some of your settings, or any files you have on the machine.

Run Windows Update again, and this time choose what you install wisely.

Niku san wa tomodachi desu.
~Chi san