run these commands to install a desktop environment:
sudo apt-get update sudo apt-get install ubuntu-desktop
You should get a graphical login prompt at that point (I'm not completely sure; if you don't get one, reboot).
Once you have a GUI, you should go and enable a few more software sources, at the very least security updates and the universe repository. Click on the Ubuntu button, and search for "Software Sources”, and check the “restricted”, “universe” and “multiverse” boxes (in addition to “main”) in the first tab, and check at least “-security” and “-updates” (and you might as well check the others) in the “Updates” tab.