Well I'm an extreme newbie to Linux. Just got tired of Windows upgrades all the time and filling their pockets with money. I have tried Knoppix but wanted to have OS permenently installed on my PC.
My son had a 5.10 version of Ubuntu so I loaded it and liked it. Wanted to upgrade, so I moved up to 6.06.1 LTS. Everyhting working fine until I took out the Nvidia card and tried the ATI agp card. Now I'm having trouble with the video.
When I first boot up the pc, everything goes fine loading drivers until it goes to the next screen which is blue and says "Failed to start the X server(your graphical interface). It is likely that it is not set up correctly. Would you like to view the X server output to diagnose the problem. I hit enter and go to the next screen and I have a wealth of info about system version,build date, build OS, etc. I see that the device is still trying to use the Nvidia GeForce 2 MX100DDR/200DDR driver. Also at bottom of screen says"Fatal sever error: no screens found. Next screen says The X server is now disabled. Restart GDM when it is configured correctly. How do I fix this? Or, is it just easier to go back to my previous video card? Its an older computer running only a 700mhz duron and the old video card was a 32mb nvidia and newer one is a ATI Radeon 7000 64mb. Thanks for any suggestions and help. Gary H. Vancouver,Wa.

You are correct, X is trying to use the nvidia drivers. Ubuntu does not bother to autodetect the videocard every time you boot up, so it assumes that the nvidia card is still in place.

When this fails, X returns an error, some info to help (which it did), and gives you a simple terminal to use to fix this.

The best fix is to get X to reconfigure for the new card. You do this my entering the following command in the terminal:

sudo dpkg-reconfigure xserver-xorg

... follow the instructions.
... and that is it.

If you want to explore further, the video and associated x server configuration lives in a plain text files /etc/X11/xorg.conf ... it is good to look at this as it usually contains a whole load of stuff you don't need.