I had a very difficult time finding a way around an Nvidia PCI card crashing my Ubuntu 7.04 install. My motherboard has integrated Intel graphics but I wanted to use an inexpensive Nvidia card. Nothing worked until I found a couple of very helpful How To pages:
sorry dead links (10-20-07):
Link 1
Link 2
Once I followed the directions my problem was completely solved.
HP Pavilion 7940: Integrated Graphics replaced with Nvidia 5200 128MB PCI
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