Probably what has happened is that since you started with XP then Vista and then Windows 7, the drive that has XP on it is marked System, Boot etc.
Using Dual Boot Pro, go to System Boot Loader Tab, and on that page place a check in the Window Vista, Windows 7 bootloader to install, and another check in the all drives and then click on the install Bootloader button.
Once this done, go to the Operating sytems tab and on that page you should have all your OS listed, make Windows 7 the default and make sure it is listed first when you boot.
Then using Dual Boot Pro again, go back to the Operating system tab, and on that page click on XP and then click on the Red X to the right to remove the listing for XP ( it doesn't delete XP only the listing for it)
Then boot again to make sure XP is removed from the choices and repeat the previous steps to remove Vista
Game Over!!!!!!!!

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