I have always had PC's but I got a MiniMac a few months back and I love it..... not possible in that price range even without a screen or keyboard though!
Pretty much any PC will do everything you could ever want to do, 2 screens are very easy to work with I have that set up at work, fantastic being able to work on 2 different programmes at the same time It's very simple to set up also, even if the PC graphics card does not support it you can get plug and play adapters to enable extended desktop.