You could also use Xubuntu instead of either of the other two. XFCE is lighter than either KDE or GNOME.

http://cdimage.ubuntu.com/xubuntu/ports/releases/gutsy/release/

I recommend downloading the Alternate Installation Disc. It has more options than the Live disc (which is the standard install) and uses the text-based Debian-installer. Don't be intimidated by Debian-installer, though....it's very much like installing Windows XP. If you've done that, then Debian-installer won't be difficult.