This one is a good article on how to place your VSTools form to the center of the screen, with respect to the Screen Resolution.
Pretty good R&D, I would say. As not many would have this on mind when they develop a Customization till they actually get a feedback from the clients. And as Daoud mentioned on this article, the clients will certainly be so annoyed if they see a GP screen showing up in the Top-Left corner all of a sudden.
A must-to-refer article from Mohammad Daoud.