
Vanna, I think I just bought myself a clue.
CPU-Z, a lovely little monitoring program, reminded me that my memory was DDR2 -- one 2 GB chip rated for 400 Mhz, and two 1 GB chips rated for 333 Mhz. DMA looks like 366.7 Mhz.
My mobo, a T-series TA790GXBE, had four DDR2 slots (which was why I got it, so I could keep my old memory) -- rated for 533/667/800. (Or, if I had an AM2+ or AM3 CPU, which I do [as mentioned earlier, it's a Phenom II X2 555 Black Edition], I can run DDR2 1066.)
(Also onboard is an ATI 790GX shared-memory graphics chip. I think it's disabled -- the only option I see is from the MSI Nvidia card -- but I'll double-check.)
Does the massmind have an opinion about whether the memory chips themselves, or more specifically their clock speeds, might be part of the problem?
ETA: More fun. This time, the retail variety.
The small indie computer store near where I live has ridiculous prices. I understand it's hard for a small store to get the discounts that big-box stores can, but these guys are really bad. Sadly, today I can't share the precise numbers with you, because none of the stores three web sites will load. Which is really not good for a computer store.
Micro Center seems to have a number of goodies I could use, at a price I can almost handle. But it's an hour away, through Friday rush-hour traffic.
Best Buy has a buttload of memory -- available online, to get there in 1-2 business days. The only chip they have in-store of the type I want costs double what the online orders cost.
Yeesh.