If you also want "contrib" and "non-free" and "non-US"
your /etc/apt/sources.list should look something like this:

deb ftp://ftp.us.debian.org/debian/ sarge main contrib non-free
deb http://non-us.debian.org/debian-non-US/ sarge/non-US main contrib non-free

To add/remove packages use the text based "dselect".

To configure a bunch of stuff at once use "tasksel".

Once you have your GUI going use "synaptic".

If you need to tweak X use (from console as root)

dpkg-reconfigure xserver-xfree86