D'oh! Well, despite this and despite a freaky error that happened once during bootup, it still seems to work alright under Windows 98. I'm not sure I'm getting 100% of its power, though. Battlefield: 1942 worked alright, so that was good.
The BeOS driver worked like a charm. Within minutes I have color again and the teapot demo shows me I'm getting pretty good frame rates.
Linux is another story. It won't even boot into X, so I'm living on the command line, trying (mostly unsucessfully) to use links. I attempt to install the rpm's it says it needs and I quickly find myself in rpm hell with requirements and conflicting libraries. This is why I don't spend a lot of time upgrading Linux - I usually just order the latest CD from cheapbytes.
I'll try again tonight. Maybe it's time for Gentoo, anyway.