It's actually pretty easy. We know a circle is 360 degrees so divide that by the number of duplications you need and that will give you the degrees to rotate. So for example, in the wheel example above if you divide 360/5, you get 72, which is the degree of rotation you want for the five holes. Here's how you go about it:
Draw your first curve shape and rotate/translate it to where you want it. Now press insert and move the shape's pivot point to the center of the wheel. Once it's centered, hit insert again to get out of pivot mode. Now go to your edit >duplicate> option box and look at the settings.
Put 5 in the number of copies and 72 in the rotation box pertaining to the axis you want to rotate around (xyz left to right).
Click duplicate and there you have it. Actually, you'll have one copy overlapping the original shape so you can just delete it. Or put 4 in the duplicate options.
"Terminat Bora Diem, Terminal Auctor opus."