ok, tried it:
I don't have /dev/agpgart ; looked for agpgart in differen locations, didn't find it.
then tried setting Option "NvAGP" "1" and later "0"
nope, it does not have any effect.
when disabling AGP, the line before the last line in the log just disappears, but that's all.... (that line is: AGP is successfully initialized)
last line: setting 1024x768...
why does that not work?