>How to determining current screen resolution, the available resolution and change it (which function & library)...?

Both of the Win32 functions GetSystemMetrics() and GetDeviceCaps() will give you the current resolution. I don't know that there's a way to determine the maximum resolution, since that would depend on the video card and the monitor, both of which may have differing maximum resolutions. Note that even Windows itself, after you change the resolution settings, will say, "well, I can try it, but there's no guarantee that it will work."

As for changing the resolution, I would recommend against it for two reasons:

a. The reason above. You stand a reasonable chance of rendering the display unusable if you don't have some checks in place.

b. Users may get a little peeved if you go changing the display settings. I know I wouldn't be too happy if an application changed my display settings at random.