I just got debian installed last night myself. If apt is already setup you could install x next w/ 'apt-get install x-window-system'
If apt-get is not setup then you must add sources to your sources.list 'apt-setup' . Then 'apt-get update', then for me it was the command above for x windows. Then 'apt-get install kde' or 'gnome' if ya want a desktop environment.. At this point i change the /etc/apt/sources.list to unstable instead of testing. then i did 'apt-get dist-upgrade'.
Once i did all this i logged into KDE and got "opera" web browser downloaded(my personal pref), installed, and mounted my windows (search for edit fstab) partition and got my mail stuff from my windows opera install. And now here i am posting this. That is as far as i have gotten.
Hope this helps,