Downloaded via steam? Yep, that'll work too. Just might require a bit of hoop jumping due to Steam wanting to be installed in the program files folder.
Just to make sure that your hardware is able to handle the game properly, you should post a dxdiag here.
Yes...you really should make sure. Don't assume that this game will just run on your hardware because it's a 5 year old game...it still make people systems cry.