It will have installed whichever version you downloaded, 32bit or 64bit.
For the graphics not working, probably the first step is to blow away the xorg.conf config file as Ubuntu 8.10 should do pretty well without it. First login with your username and password on the CLI screen and then
sudo rm /etc/X11/xorg.conf
and note that it will ask for your password again. Now restart the login process
sudo /etc/init.d/gdm restart
and see if it works. If it doesn't
and post the contents of that file to this board and we'll try and get you going again.