Change Gnome login background/theme

1.When logged out, hold down CTRL+Alt+F1
2.Type export DISPLAY=:0.0 and press ENTER
3.Type Sudo -u gdm gnome-control-center and press ENTER
4.Hold down CTRL+Alt+F7
5.Gnome Control Center will appear. Press ''Apperance'' and choose a picture.
6. Close the window and log in

Gnome + Xmonad

From http://markhansen.co.nz/xmonad-ubuntu-lucid
Here’s how to run XMonad as a drop-in replacement for gnome’s default window manager (Metacity):

Install XMonad. Open a terminal and enter:

sudo apt-get install xmonad

Configure XMonad to interact happily with gnome. Make a file ~/.xmonad/xmonad.hs, and put in it:

import XMonad
import XMonad.Config.Gnome
main = xmonad gnomeConfig

Compile this config file by typing xmonad --recompile at the terminal.

Tell gnome to use xmonad instead of metacity. At the terminal, enter:

gconftool-2 -s /desktop/gnome/session/required_components/windowmanager xmonad --type string

Log out and log back in and you're done.

NOTE: To revert back to Metacity from XMonad, at the terminal, enter:

gconftool-2 -s /desktop/gnome/session/required_components/windowmanager gnome-wm --type string