Well its filmed in Second Life. You might think that Steve must have been a dab hand with the editing. However, many of the objects and sometimes even the avatars can be bought. They are called artifacts. So the TARDIS and the Star Trek Next Generation transporter were both coded by others and are available to be bought in Second Life.
The currency is something called Linden Dollars. They have a really low real value, but in Second Life can buy many things to improve your appearance etc. The only limiting is the computing power in showing the better quality objects. this is a world much as envisioned by Tad Williams in his Otherland series of books.