Shaz, right clicking on the background (wallpaper) should let you access to either nvidia or catalyst (radeon) control center if your graphic driver is updated, but if you can't get there, right click on the background and go properties in xp, or Screen Resolution on 7. There should be an option to change your primary monitor.
edit. Oh wait, this doesn't fix your problem
Open control panel as mentioned above.
Press alt+space+m. Its hotkey to move windows. Hold mouseBotton1 and drag windows to your second monitor.
Apply whatever settings.