RH created this "problem" themself. Since it isn't a great idea to use drivers compiled using a different gcc version, RH made a patch for modutils. The version of modutils RH uses now is 2.4.18-2. A short time ago they used 2.4.18-1. The only difference between those versions is a patch that checks for gcc 2.x code in modules when they're being loaded under a 3.x built kernel.
To realfix for the problem will be new driver packages from nvidia since mixing drivers compiled using different gcc versions can cause strange problems.
For now the fix is to switch back to modutils 2.4.18-1 from RH or to compile a modutils from source (for example 2.4.19).