So far all the advice/suggestions I've been able to find online is to up/down-grade drivers, which you've already tried...

Damn. I know I'm grasping at straws here, but, since I don't think it's clear what exactly is causing the bug, do you think it might be worth trying to use different DirectX versions ? I don't know about RTW, but MTW is old enough that you should be able to have a bit of leeway varying the DirectX version... As I said, grapsing at straws, I admit it... but I don't have any better ideas.

I've looked at the VIA fix... in what way does it not work for you, is there just no effect ? I guess you tried it in combo with different drivers, as well ?
I realize I might be grating your nerves, if that's what you've been going through the whole night before, but I'm afraid I don't have anything better...

If there are any combinations of drivers with the VIA patch and maybe DirectX, as well as BIOS settings, that you haven't tried yet, maybe it's worth a try...
Also, I saw one guy said you shouldn't allocate too much PCI texture memory ? Did you try to fiddle with that, decreasing it as much as you can ?