Installed Media Center 2005 upgrade: Having some problems

First off, thanks for taking the time out to look at this. Here's my problem:

I installed the 2005 upgrade from my HP media center 2004. It was working fine for about 2 weeks. Now all of a sudden my system is very sluggish, often freezing for about 2 seconds at a time. Also, when I try to open programs now (firefox / AIM / etc..) it takes over a minute for them to open (rather than a few seconds like it normally does). I've tried the following to fix this.

cleaned registry (CCleaner)
ran virus protector (Norton) (No viruses)
ran spyware programs (No spyware detected)
Installed all the latest windows updates

None of this helped. If anyone can help me fix this problem I'll be in your debt forever!

(HP Media center 2005 XP/ 3.2 ghz pentium 4 / 1 gig of ram )

Thanks guys,

Joe

running "spyware programs" does not mean you are clean, adaware and spybot are free but it does not mean they do the same job as spysweeper, so run spysweeper to be sure then post us your hijackthis log here