Computer Monitor & TV setup help.

[DrewSG3]

I got my TV hooked up to my computer, but I'm having a problem trying to get my desktop to be displayed on both at the same time. If the monitor has the desktop sized correctly, the tv will only display part of the wallpaper. It also seems the mouse will go over from desktop being displayed on the monitor to the TV

I have the monitor set at 1280x1024 and the TV set to to 1920x1080

It's worked before, I can't figure out what's wrong now.