What version of gcc are you using?
I have a Geforce4 TI with an NForce2 motherboard and for some weird reason, AGP was listed as being disabled when using the 4191 drivers too. I had reverted back to the 3123 drivers temporarily and it worked (only at AGP 2x), however after upgrading to gcc 3.2.2, I was able to get AGP working properly at 8x. I'm not entirely sure it was the upgrade to gcc 3.2.2 that fixed the problem, however I can't think of anything else I changed that would've had that effect.
AGP Rate: 8x
Fast Writes: Enabled