Here's what I'd do; 
I would suspect faulty hardware as the first thing, so I'd have to somehow check it. 
-A full, all sector scandisk (bootup might have overlooked something a full scan will not). 
-Memory since you have 2x ram chips, put one on, then switch to the other, see of problem goes away. 
-Video card, try another one (maybe you got an old one laying around?) 
 if you still haven't found anything, pull out/disable all possible hardware (LAn, Modem, etc. I've seen a faulty modem create problems like this. If problem goes away, add hardware back one at a time, tell you se the problem again. 
Usually I snagged the problem by then. 
I suspect you might have bad memory either video or ram, but could be any of the cache. 
You can run one gig with the 2 gig kernel, it should be ok for testing 
		
	
		
		
		
		
		
		
		
		
		
	
		
		
	
	
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