So I have just uploaded the NVIDIA drivers for 2.12, both "legacy" and latest. I have tested both, and they work fine. It appears that "legacy" applies to all cards up to PCI ID 0x0153.
Both of these drivers depend on agpgart.ko.

One little fix required - with some NVIDIA cards (the older ones I think) Puppy automatically loads the "rivafb" module at boot up. This module will block the nvidia module from loading, and X will fail.
My (rough) solution was to add "rmmod -f rivafb" at the start of /usr/X11R7/bin/xwin
You might be able to come up with a neater solution.

Apart from this little problem, the setup is the same as before; for xorg.conf

In Section "Module"
REMOVE
Load "dri"
Load "GLcore"

ADD
Load "glx"
Load "dbe"

(Puppy's xorg.conf is already like this)

And in Section "Device"
CHANGE "nv" to "nvidia"

And I have a new version of MPlayer almost ready. I'm testing it at the moment. XvMC for NVIDIA now definitely works!