I do the exact same thing, and have almost the exact same problem, so you're not alone.
Does your monitor have an "Auto Adjust" button on it? If so, every time you switch, just press the auto adjust, which fits the image properly on your monitor. As masonm said, a video comment might help.
I don't think it's our monitors that do this, I think it's more the fact that Linux and WinXP use different positioning techniques but I could be wrong.
Anyway, I hope this helps