Buying Civilization 4 the game?

I want to buy Civ 4, because my dad bought me Civ Revolution and i really liked it and i dont want to buy Civ 5 just yet. I'm wondering if i should get a digital download or buy a disc, and how i can make it run on Windows 7. Cause i hear alot of people have trouble with that. And if i should get a disc copy, where could i find one??