Snow Leopard Freezes, Reboots, Crashes, Kernel Panics

I have a Unibody MacBook Pro 15 inch, late 2008. I got it with Leopard, and I had absolutely no problems at all with it until I stupidly upgraded to Snow Leopard in September 2009. Since then my computer crashes a lot. Here is a list of problems I've had so far, most of them on seemingly random occasions:

- Kernel Panics (happened around 2 times, both while rendering a video in Final Cut Pro)

- Complete system freeze where the screen freezes on the last thing displayed, the last sound played keeps looping (if I'm in the middle of a Skype conversation or listening to music, for example) and nothing will react (including mouse, caps lock, eject key, the system won't even sleep when I close the lid) requiring a hard reset by holding the power button (happened at least 3 times). This has sometimes happened when all I was doing is listening to music on iTunes, I wasn't even touching the computer, and all of a sudden I just hear the last half second of music looping forever.

- Complete freeze where the mouse would still move, but the system would reboot automatically after a few seconds (happened once or twice)

- Reboots without any warning (happened around twice)

Basically these are my major problems, and all of these have happened in 10.6.1 and 10.6.2, except the kernel panics which have not happened (so far) since I updated to 10.6.2.

I have tried repairing permissions, it didn't change any of the above behaviours.

This is what I noticed:

These problems happen regularly, around one or two times week.

_*The problems only seem to happen when I set my computer to use the dedicated graphics instead of the integrated graphics*_ via "System Preferences > Energy Saver > Higher Performance". If I set that setting to "Better Battery Life", then the problems don't seem to happen at all.

However, I use Photoshop and Final Cut Pro a lot, so I need to set the graphics to +Higher Performance+. Dedicated graphics is one of the reasons I bought this computer, so setting it to Better Battery Life isn't a solution for me.

As I've said before, I'm running OS X Snow Leopard 10.6.2, and my machine is a late 2008 Unibody MacBook Pro with 4GB RAM and processor of 2.53 GHz.

I have performed an upgrade to Snow Leopard from Leopard, as opposed to a clean install. Trying a clean install of either Leopard or Snow Leopard will be my last resort if nothing else works, however, I am asking you whether you can think of anything else to solve my problems without having to do a clean install, as it would require lots of work and it would be a big hassle for me.

Thank you very much.