The same problem exists here. I have fresh (null) distribution installed, with gcc 3.2. The driver compiles ok, but refuses to install. The error message is coming from insmod, complaining that the nvdriver is compiled with gcc 2 while the kernel is complied with gcc 3.
In my case this simply is not possible since there is no gcc 2 in my machine. My suggestion is that this has something to do with the precompiled binary that comes with kernel module package. If its format is different from gcc 3 format, then it might cause this kind of touble.
And yes, I use my own compiled kernel 2.4.18 with the very same gcc 3.2-1