Computer memory question?

Question: If you were to download and install something on your computer, say an online game like WoW, or LoL, or HoN, it takes 501 MB to download (not actual number). You then have 501 MB less space on your hard drive. If you were to uninstall that game/program, would you get that 501 MB back? Also, if you don't get it back, and you download/install the game a second time, is that taking 1002 MB (becasue the 501 MB x 2 downloads)?