Need help fixing a possible background problem in a windowed browser

[BC23]

Hello!

I was wondering if anyone could help me fix a problem I am having with my website.

http://i22.photobucket.com/albums/b344/BranCarr/link.png

As you can see if you are in a windowed browser and move right, something goes wrong.

Where is my best place to start looking to fix?

Thanks!