When I clicked O (Open Data file) the screen just flickered. Also, the Change Graphics Dialogue would only open the Ltg's in the LaserTank folder, the three that come packaged with the download. The Change Directory button causes an error message. By the way, this dialogue box has never made sense to me; the internal graphics and user graphics boxes seem unnecessary to me.
Anyway, to view other graphics, I simply delete the three that come packaged with the download and replace them with three (the seemingly maximum) I want.
In order to open other level files, I clicked the Disable Warnings tab in the Options menu, and can now open other Level files. All this is with my UAC turned off. I'll try it again with it turned on to see if it works in that mode.
Gerry