MBP freezing/slowing down

I recently got my MBP (5,5; Sept, 2009) back from the Apple store. I had had some start up problems, diagnosed it as a bad HDD (despite Disk Utility's insistence it was okay), which was confirmed at the Apple store and fixed. It was returned running 10.5.7 (dropped off with 10.6.2 :/ ), and I tried upgrading back to 10.6 with the install disk. It gave me an "Install Failed" message, and showed the "no startup disk available" when I restarted. I booted up from the Install disk and formatted the drive in Disk Utility. I tried installing (several times), getting "Install Failed" messages or having it stall/freeze. Finally, I was able to get 10.6 installed, and it seemed to be working well.

Since then, however, I've run into some issues. My computer will rather regularly freeze up and display the "pinwheel of death". It usually happens in Firefox, or when using Spaces. Also, iTunes will sometimes pause for a moment and then resume playing. I'm usually running Firefox, iTunes, Sunbird, Geektool, Quicksilver, Google QSB, and a few menu apps (insomniax, caffeine, smcfan, and alarm clock).

When the pinwheel comes up, I can usually still use Spaces, and the mouse returns to the regular cursor when I move away from Firefox (or whatever I'm in), but I still can't click on anything else.

Any idea what could be causing this? I've cleaned the caches with Onyx, and done everything else I can think of, and the problem persists.

**Sorry about the length of the post, I just wanted to cover all my bases as far as troubleshooting questions.

Have you tried downloading and installing this. It can often sort things out.

Is this a further step from the original 10.6.2 update? I've already got that installed, but I'll give that a shot if it's something new.

Not something new as such, but all the previous updates in one package which covers scene where incremental update has left a flaw.