I've seen a number of people who had this problem, so here is a solution that worked for me, tho it is involved ...
Asus M3N72-D motherboard
AMD Phenom 9950 Quad-Core Processor
8 gb RAM
2 Samsung HD501LJ 500gb hard disks
Dual GeForce 9800 GTX+ video cards
First, open Synaptic and make sure the following packages are installed:
linux-headers-2.6.28-11.42 (assumes you use the current kernel)
Next, make sure the following are NOT installed, and use the "Mark for complete removal" option if any need to be removed:
ALL nvidia pkgs (search for nvidia)
Any old kernel pkgs, ie linux-headers-2.6.27-X and earlier
(This might not be necessary, but I did it anyway)
Now, perform the following command in a terminal:
sudo lspci | grep VGA
The output will look something like this:
02:00.0 VGA compatible controller: nVidia Corporation GeForce 9800 GTX (rev a2)
03:00.0 VGA compatible controller: nVidia Corporation GeForce 9800 GTX (rev a2)
Write down the number begining each line (the 02:00:0 and 03:00:0 or whatever your output shows).
Go to System-Administration-Hardware Drivers and choose 180.44 and activate the driver - DO NOT REBOOT yet!!!
<If you have nothing to activate in hardware drivers, then go to Synaptic and install:>
Open terminal and type:
sudo gedit /etc/X11/xorg.conf
Replace the graphics "Device" section with the following:
Identifier "Configured Video Device"
Edit the BusID line to reflect the number you wrote down earlier (for me, that would be "PCI:2:0:0". ***MAKE SURE*** you use all colons as shown (the original line you copied had a period before the last zero), and add the PCI part as shown.
If you have sli, add the following line after the driver line:
Option "sli" "auto"
Save the file, reboot and you should have 3d graphics working.
***NOTE*** - for dual graphic card PCs, you may boot to a black screen but you'll hear the normal boot sounds. If that happens, use the other number you got from earlier OR plug your monitor into the other card.
This got Nvidia's restricted driver working for me after a number of other solutions failed. After this, upgrading within Jaunty releases should go smoothly, but save this in case the next OS update screws you again.