Since when did this turn into a topic for posting your own computer specs?
On topic: Judging from all the specs you posted, I'd agree with keonesan, just get a new computer. It's not worth the money to upgrade all that stuff when you could just get a super awesome one for much less.
And yes, get Windows 7, it's excellent.
I'd personally recommend an Intel i5 or i7, at least 8GB of DDR3 RAM, and an HD NVIDIA graphics card.