I replaced my card but I'm not sure how to set things up on Ubuntu.

When the computer boots, it doesn't start GDM (I think that's what it's called). Instead, it asks me to log in the command line. If I try to do a startx, it tells me there is no AMD device connected or something to that extent.

I originally installed the ATI drivers using the GUI. It said that I was using the limited drivers or something to that extent with a popup on the right of one of the taskbars, so I clicked there and updated it. I think it could also be reached by going to system > administration > restricted drivers or something close to that.

I tried installing the nivida drivers by doing a "sudo apt-get install nvidia-glx-185" and then doing "sudo modprobe nvidia" and "sudo nvidia-xconfig" as this guy says but that didn't work. Modprobe couldn't find anything related to Nvidia and nvidia-xconfig wasn't an available command for me. Since I wasn't sure how to remove the ATI drivers I did that without messing with them. Not sure if that was a good idea.