Just for posterity's sake-

I finally found a clue that led to functional drivers for this machine on Windows 2000.
Sony couldn't point me to them on their own site- all they could say was that none existed and as soon as they were published they would be available. Yah- a ten year old system and a ten year old OS upgrade will be revisited for updates, soon... riiiiight.

As it turns out, though, stepping backwards one model number *does* allow for driver updates wrt Win2k. I downloaded the ATI driver updates for the PCV-L630 on Win2k and they were good enough to work without a problem while retaining the original monitor- PCVA-15XTAP2.
Yay!

Still having a problem with the second memory slot, though. Perhaps I'll have to try a variety of stick combinations before I find something that the machine is happy with. Until then it's stuck on 128MB- ugh!

Thanks again to everyone for their support and interest!