Need to make this system better/more stable....

Ok my current system is about two months old and I'm somewhat frustrated with it. I use it mainly for gaming (WoW, CS, Q4, and Q3 mostly) and I leave it on 24/7. I've had a few stability issues with it and I can't quite figure out exactly what causes some of these problems. It's gotten to the point to where I'm considering just starting from scratch with a new build but I haven't given up hope on it yet. I'll list a few of the problems and my specs below.

A few times, my computer has completely frozen while playing a game, or just doing almost nothing at all. None of my hardware responds and there's no real cosistent pattern as to when this happens. I'll have to manually turn it off and turn it back on.

Several times I've gotten BSOD's. One of them said "IRQL_NOT_LESS_OR_EQUAL" or something similar to that.
Also, about two nights ago, my computer was running very sluggish, so I turned it off for a few minutes. I went to turn it back on and at my POST screen, it displayed many badly rendered, glitchy, somewhat bar code looking squares on my screen. After the POST, there was a BSOD but I couldn't figure out what it said because of the artifacts on the screen. (I'm assuming they were artifacts caused by my video card and heat problems with something in my system but I could be wrong)

The heat with the processor is a concern of mine. It idles at about 50c and gets up to about 60-61c on a full load.

MSI P4N Diamond
P4 630 - 3GHz, prescott core (running on stock cooling)
1GB Corsair XMS2 DDR2-667 (PC5400)
BFG GeForce 7800GT OC
Ultra X-Connect 500W

So I ask you guys here, please help me in any way you can with these problems. I'd appreciate any help I can get with this system.

I've read that before and I hope it's just heat, if anything, that is causing these problems. Thanks for the suggestion though. I'm just trying to determined if it's more than just heat and what exactly it all is. If it is just heat, I'm definately going to probably get a Zalman CNPS9500 for cooling..