>In the last hour I found some posts on hardware support sites where people were running into identical or nearly identical problems. Seems that in many situations, disabling Fast Write/Write Combining solved the problem.
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>I also saw a reference to a bad RAM chip, and also to situations where people added onto the laptop to the point where the laptop overheated and caused video problems. I haven't added any peripherals, so that last one doesn't apply to me. So I'll check the links you sent, and I've disabled fast write. If I don't run into any problems this weekend (this has occured every day for a month) and the diags don't detect any problems, then maybe that setting was it.

The best memory test program out there can be found here: http://memtest86.com/ get the cd iso image and burn it, run the program for several cycles, if not hours.