I think you can try some old proprietary driver for example 173 or 304.
sudo apt-get install nvidia-173
I should also ask about the computer specs: CPU and RAM.
sudo apt-get install nvidia-304
If the computer specs are too low, your solution could be to get a lighter desktop environment and continue with nouveau.
Try Lubuntu or Xubuntu.
I'm using a fairly cheap nvidia card that works well: GeForce GT 430
and I use the following proprietary driver in Ubuntu 12.04 LTS: NVIDIA 304.88 (nvidia-304)