No ideas, but at least i'll tell you that you're not the only one, i've the same problem with totally different configuration, (Athlon Via KT133 with Riva TNT2), and look at the post "please help", I think that it's the same issue, and even i found other older posts with same sympthoms, lockup at startx when AGP activated, and the log file truncated at the Initializing "xxxxxxx" mode line.
I've found no solution to this problem anywhere, I've tried the last Mandrake and Redhat distributions, and even I installed FreeBSD with its drivers, I've got the same sympthoms with all this configurations, It has to be a bug of the drivers that is present only with some hardware. I wrote to the Nvidia technician support by mail but I got no response. It's not a hardware fail becouse the AGP is working without any problems in W98.
Well, I suppose will have to wait Linux to be a majority O.S. to get fully supported drivers and tested with all kind of hardware...
P.D: excuse me for the my english