I'm not saying it's a good solution, but if the problem is within the nvidia binary driver there is little you can do.
Well, if I look for support on the nvidia site it points to this forum. So hopefully this thread get the attention of some expert at nvidia who can tell us how to solve this problem or who can make sure that the next driver they release does provide working HDMI output.
I'm also using Ubuntu 8.10 and have minimal options in xorg.conf and saving xorg.conf works fine here. Try posting it and let's see if it can be worked out...
This is my xorg.conf at the moment, but as I told before: Fixing the problem that 173 gives doesn't really solve anything for me. There is no HDMI audio, so using windows when I want to watch a video works better for me until this problem in 177 is fixed.
Identifier "Configured Video Device"
Identifier "Configured Monitor"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
Option "PixmapCacheSize" "5000000"
Option "AllowSHMPixmaps" "0"