Wallpaper doesn't fill second monitor

Hi everyone.

This is kind of a minor issue but there is a user asking about it and I don't have an answer.

It's a Windows 7 laptop connected to an external monitor with the laptop display set as the primary. On the external monitor, the background doesn't fill the screen, there's a big black border around it. I played around with the different settings and nothing seems to work.

If it's on the external monitor only the wallpaper looks fine, it's only when both displays are up that there's an issue. I'm told that she didn't have this problem on her Windows xp machine.

Is there a fix for this?

Thanks.

Chris Hansen