GetDesktopDisplayMode(index, ByRef w, ByRef h, ByRef freq)
Gets the resolution and refresh rate of a display
index - The display index (ie. if you have 3 displays then index could be 0, 1, or 2)
w, h - The width and height of the display will be stored in these variables
freq - The refresh rate will be stored in this variable
Example:
w = 0
h = 0
f = 0
GetDesktopDisplayMode(0, w, h, f)