This may have done it.
I switched the RAM from the top two slots to the bottom two slots. Yeah, I did RTFM, a few times. The problem was I MISREAD the part where it says the RAM slots are numbered from BOTTEM to TOP... I read it as TOP to BOTTOM.... So, I'm feeling about as stupid as possible.
On top of all this... I was still chasing hardware errors. My old Corsair XMS3200-C2PT RAM runs FINE at 2-3-3-10, T1, and it's only rated for 2.5, so I figure I'm doing quite well. Survived endless SANDRA burn-in tests w/15 web browser windows open and some background tasks running, which had previously caused system crashes. No errors now whatsoever. In contrast, the XMS3200-XL (rated at 2-2-2-5) still crashes.
I'm not spectacular at understanding the memory timings, but my understanding is that the important numbers are the CAS (3, 2.5, or 2) and the T (1T or 2T) timings (for AMD systems)? So, is it safe to assume that, for a primarily gaming/web-surfing rig, I would notice very little, if any, difference by upgrading the RAM speed (I'm running 1GB, and wish to stay at that size)?
Thanks again for all the help from everyone here... without all of the feedback/input, I'da given up long ago.