i all. I have the same problem, but i'm found the temporary solution:
1. Insert LiveCD with Ubuntu 10.10(or Kubuntu)
2. After loading menu of CD press F6 and set "nomodeset" option
3. Click "Install ubuntu"
4. Loading and installing must be successfull
5. After post-install rebooting system in GRUB menu select first string and press "e"
6. After words "quiet splash" write "nomodeset". Result must be "quiet splash nomodeset" (without quotes)
7. Click Ctrl+X
8. The system must loading successfull
9. Install new videodriver(Ubuntu must offer this or install from Nvidia website) and reboot the system
Disadvantage: splash screen with "Ubuntu" and "points" now a low quality:)
Tested on Ubuntu 10.1032 bit , Kubuntu 10.10 32 bit. Hardware: Nvidia GT240 1024Mb DDR5 PCI Express 2.0

Thanks for attention