I recommend the OP to wait till this xmas for the OnLive machine.
If it works as the manufacters hype it, it will be worth it.
If it doesn't meet the expectations, you can go ahead building your PC, and by that time you will know that it is the right thing to do since onlive service is not worth it, and also the hardware you want will be cheaper. You can have the PC you want right now for less money, or spend the same amount of money on better hardware.
Just wait and grab an icecream! =)







