Have you considered putting one together yourself? It is actually pretty simple (man lego) and it means you get more kit for your money.
Here is a very well written guide that takes you through the process. If you do want to go down this route we would be happy to give you a full parts list that can just be assembled and meet your needs (ie mainly gaming).
Alternatively, if you don't want to build on yourself I would suggest going for
this (+Windows 7 Home Premium 64 bit OS and 5850 graphics options) and add a good gaming mouse like
this. This would be a much better gaming system that the one listed in the 1st post and this one also has significant upgrade potential (add a second 5850 in the future if you wish).