Spiderdim wrote:thanks for the answer guys!
so only linux!
That is the simple answer! You will find a wide range of Linux variants available for the Pi.
The more complicated answer is that you need an OS that can run on the ARM processor and has been ported to the Pi. The main non-linux one that springs to mind is RiscOS although there has been talk of others becoming available.
There are others in early porting mode such as Android and Free BSD that are similar but are not strictly speaking Linux. I think Andoid will be of particular interest to a lot of people - particularly with the release of the Pi Model B with 512MB which should mean it can be made to run with adequate performance.