I suggest you follow the instructions to revert changes in this guide. Additionally, go to Synaptic, click Status -> Installed (Local or Obsolete), and ensure that you don't have any xorg/mesa/drm packages listed in this section. If you do have driver packages listed in this category, do the following for each: select a package, go to the Package menu, choose "Force Version...", and pick the default Jaunty version of the package. Providing that there's no conflicts, apply changes, and then log out and back in.
Hmm. It's just that, GNOME (and KDE) isn't usable because I just see a white screen background. Any suggestion, sir?
MacBook Air 3,1 128gb | Fujitsu Esprimo U9200 | Google Nexus One