I've had this lying around for a while, and to make matters worse I've now ride myself of my GeForce card.
But here goes:
Part one - tweaking the nVida drivers.
This requirtes you to use the tarred driver source, it will not work with the binary packages, since we will be editing the source a bit.
download the lastest drivers from the nvidia website:
now unpack, and enter the directory
tar xvzf NVIDIA_kernel-1.0-XXXX.tar.gz
now comes the fun bit, editing the source:
vim os-registery.c (I use vim, feel free to use you favorite editor)
As you'll discover the code is very well commented. But I'll highlight the important bits:
change this from 0 to 1 to enable AGPx4 on VIA chipsets. This should be safe if you use the mem=nopentium workaround in grub or lilo to avoid AMD chip related crashes.
U032 NVreg_EnableVia4x = 0;
change this from 0 to 1 to enable AGPx4 on ALI chipsets. (please report the outcome of this to me - I haven't had the chance to test this one yet)
U032 NVreg_EnableALiAGP = 0;
change from 0 to 1 to enable AGP sideband adressing. Do a cat /proc/nv/card0 to see if your card has support for this feature, if it does, by god why not enable it - this may or may not increase speeed.
U032 NVreg_EnableAGPSBA = 0;
Important bit of the output from /proc/nv/card0
------ AGP Info -------
AGP status: Enabled
AGP Driver: AGPGART
Bridge: Via Apollo Pro KT133
SBA: Supported [enabled] <<-- Sideband adressing
FW: Supported [enabled] <<-- FastWrite
Rates: 4x 2x 1x [4x] <<--- AGP speed
change from 0 to 1 to enable Fast Writes. Do a cat /proc/nv/card0 to see if your card has support for this feature, if it does, why not enable it - this may or may not increase speeed.
U032 NVreg_EnableAGPFW = 0;
Part two will look at nvclock and how to use it to overclock your card