Well I pulled the 5900U out and put in a 5600U, used the 1.0-4499 drivers (since the readme for the AMD64 driver supports the 5600U) with NvAGP option set to 1, and it seems to work. I get about 2,800 FPS in glxgears.
I do have a message I don't understand in the XFree86.log:
(WW) NVIDIA(0): Failed to verify AGP usage
(II) NVIDIA(0): Setting mode "1024x768"
(II) NVIDIA(0): Using the NVIDIA 2D acceleration architecture
(==) NVIDIA(0): Backing store disabled
(==) NVIDIA(0): Silken mouse enabled
(**) Option "dpms"
(**) NVIDIA(0): DPMS enabled
(II) Loading extension NV-GLX
(II) Loading extension NV-CONTROL
(==) RandR enabled
Is this line "(II) NVIDIA(0): Using the NVIDIA 2D acceleration architecture" normal? And is 2,800 FPS about normal?