hm... well, blackbox is a very 'lite' and nice windows manager.
download the tarball from its website and follow exactly as the readme file says. i can't remember its website, but u can type 'blackbox windows manager' on the google search engine and it'll turn up.
a coupla simple commands to install it and you're got yourself a new windows manager.
oh btw, windowmaker is also very nice. and its a lot 'lighter' than gnome or kde.