Hi Kari, Et al
The problem here is that to calibrate the screen you have to click on all four corners in order so wherever the taskbar is it will interfere with at least two corners that you need access to.
There was on earlier windows versions option to not have the taskbar "always on top" If this is duplicable in windows 7 this would be solve this issue
Unfortunately I can find no information on this option or any other similar registry entry
The on top nature of the taskbar can be overridden as running Opera for example in full screen mode allows you to click on any corner to the very edge - maybe a way of making the calibration screen full screen in the same way is the way to go?