I have the same issue on four pc's:
FX 5700 LE (Slackware)
6600 GT (Linuxfromscratch)
6800 GT (Linuxfromscratch)
With every driver newer than 1.0-9639, when i pass from X to any TTY, i get corrupted screen (either with VESAFB or with plain VGA): characters are colored blocks.
Despite this, TTY's are still functional (i can blindly type commands).
Any chance to get this corrected in new drivers? In this forum there are lots of posts like this, but no solutions are given.
NVIDIA Men, are you alive?