If you would like setup Debian Linux with a very small installation then all you have to do is boot off the NETINST CD and choose NOT to use a mirror. This will install a very minimal system. Which not only takes up very little disk space but is a little more secure.
If you later want to install Gnome, but again only do a base install then all you need to do is run:
apt-get install x-window-system-core gdm gnome-core
This of course assumes the you have apt-get is installed and working.
This basic install doesn’t include a web browser so you might also want to do:
apt-get install firefox