Hmm... how to put this... I have the same mb, and I have Slackware 9.1. With both the most recent and the older nvidia drivers, I've not had any issues with compilation or loading of the module. Of course, I also compiled my own kernel, which might be your problem.
I can't say how the default kernel was compiled, but you'll have much more sucess generally if you use the same compiler for the kernel and the module. Are you sure you have gcc 3.2 installed and not 2.95? I'm fairly sure that 2.95 has been put long to pasture, but that's about the only reason I can think of you having that error. Either way, best of luck with it, slackware isn't exactly the easiest to play with on your own