Ubuntu – System not reaching login on GUI

Yesterday I finally got around to upgrading from 10.04 to 11.04 (I'm very forgetful about such things). I did an upgrade through the update manager, first to 10.10, then to 11.04. Unfortunately, I've run into an issue, stemming primarily (I believe) from the fact that my hardware doesn't seem to support Unity.

When I boot my machine, I get a screen that looks like this one (linked because the original image is kinda large). It stays on this screen indefinitely, with no animation, no mouse movement, no dialogs, etc.

However, I am still perfectly able to connect to the machine via SSH, and even create NoMachine connections with a Gnome session running on the computer. So it isn't freezing, it just no longer presents a working GUI frontend on the primary monitor. Needless to say, this is inconvenient. So I'm going to purchase a Unity-approved graphics card for the beast, but I'm wondering if there's anything I can do in the meantime, to get a Gnome or Xfce session going when I'm at the physical machine. Thanks to SSH it would be very easy for me to manipulate config files.

EDIT: Information about my graphics card:

$ lspci -v | grep VGA
  00:10.0 VGA compatible controller: nVidia Corporation C73 [GeForce 7050 
  / nForce 610i] (rev a2) (prog-if 00 [VGA controller])