Not sure if it's exactly the same problem (I never saw the strange characters you reported), but I did get lots of X freezes, also un-recoverable.
Sounds like we both tried the Ctrl-alt-smash-all-keys option, though, to no avail...
As you reported, I got itworking with the "NvAgp" "0" option, but also I had luck using the option which forces nVidia AGP; if I recall, this was the "NvAgp" "2" option.
In any case, the default (NvAgp "3", per the docs) which forces the kernel-based AGP to be tried first, NEVER worked for us...
It was elusive, too, as the module gave every apperance of loading normally, then would crash intermittently.
I'm hesitant to make predictions, especially about the future...
- Niels Bohr