Give a different kernel a go before you totally give up. Get rid of the proprietary nvidia driver and set up X through PPC with the nvidia driver from Synaptic. If you can't log in to a GUI run XFdrake from the console. It should actually be offered as an option if X doesn't launch.
As Mélodie pointed out, there are a number of alternative kernels on offer in Synaptic. Install one and set it as default in boot options in PPC, or just choose one at boot up. DON'T UNINSTALL ANY!! Did an install/uninstall at the same time once and totally borked my system
. Don't worry about using an "old" kernel. Some distros use the latest, some stay a bit off the pace. I think Debian still runs 2.6.32 or 2.6.33.
I have a TNT2 card in a P4 which works fine, so don't be in too much of a hurry to toss it. Good luck.