You can replace the default background image of your contact list very easily.

1) Find the image of your choice. 

2) Go for pictures with white backgrounds or cut objects out of their backgrounds, because dark colors will conflict with the MSN Display Names on your contact list. Also avoid very large images (resize to around 200 pixels width and/or height if possible). Finally, when possible, make it a bit transparent (eg. 40% opacity in Photoshop).

3) Save the image it as lvback.gif with 256 colors, in your MSN Messenger program directory (usually C:Program FilesMSN Messenger).

4) Sign out and in again (or switch tabs and then back to your contact list) and you'll see your fresh MSN Messenger background!