Although I agree with Europa with regards to streaming non-itunes content through apps like Air Video etc. I have an uber simple setup running at home. I've setup a public folder on my windows server at home, it'll run off any Windows laptop and you can set it up to look at Mac as well. But in this instance the Windows route was just as easy. I use the Media Player which gets installed when you jailbreak the ATV, type in the address of the public folder and boom... you're in. It'll play pretty much any format and took me about four minutes to setup...
Plus the VNC feature is kind of cool as well, it's sort of like Remote Desktop but for your ATV!
