Dune 2000 was released in 1998 for Windows 95. If you have Windows 7 Ultimate, Enterprise or Professional you can download Windows XP mode and that will probably allow you to play the old game. If you have Windows 7 Home Premium I think you are out of luck.
The friendly folks over there created a modded version of the game that works just fine in W7 64. It also features some minor improvements, such as the ability to play any mission in the campaign by selecting it from a menu. Well worth checking out.