Can I ask for an advise here too?

I would like to buy a Mac Pro so I can use both PC and Mac. My main poiont is to use it for watching HD movies and also downloading movies. I know that iMac can do that too, but iMac always get hot when you leave it on for a long time. I'm looking to leave it on 24 hours, does Mac Pro okay with that? Can someone also advise if the GeForce 7300 is okay to play HD movies? I"ll connect it with a HD Projector.