Burnt off some of the excess energy last night trying to get the new video card working (there were some posts to the gentoo amd64 list that suggested the problem might be solved by updating to the ~amd64 drivers). No such luck.

Still, got the desktop running with the vesa driver so that I don't have to physically uninstall/reinstall every time I want to work on it. The flicker would drive me nuts eventually (not to mention the incredibly slow drawing), but hopefully I'll actually get the nvidia driver working now that I can work on the machine while I'm trying new approaches to the problem.