Cpu jammed up after sp2 install

Hello all... okay, here's the deal - I installed sp2 twice, the second time I
made sure to try to do a nice "immaculate conception" install; cleaned,
diagnosed, defragged my hard drive, said three "hail mary"s and gave to the
poor box.... Both times, the install's apparently went fine, but afterwards
my computer would dramatically slow down, and upon checking task manager,
random processes would be slurping up all available cpu cycles, keeping my
cpu hemmed up at 100% usage. As mentioned, it would be random processes
doing this, sometimes my web browser (Firefox) if it was open, sometimes it
would be rundll32, sometimes msgsrv32. I could never figure out any rhyme or
reason to it. I know that one of the security features in sp2 involves
limiting application access to the cpu - could this be backfiring somehow,
maybe because I've got an older system? It's about 4 1/2 yrs old with a
Pentium III 933 mhz see-pee-you. If anyone knows anything about this, info
would be greatly appreciated.