Debian 5.04 works, after some doing. You get the same magenta screen on first startup but Debian has a trapdoor on the X server: if X doesn't start in time then init drops you into a command shell.
Which is very convenient, since you can then log in as root, run "Xorg -configure" and follow instructions. Move the new xorg.conf in place, restart, et voilà: a working albeit somewhat slow desktop.
On Ubuntu this doesn't work, apparently because Xorg can't find the nVidia drivers (you can get into a simple CLI shell via the installation disk).