If you're weak in the hardware department but you're strong with internet bandwidth, then OnLive could be the gaming solution for you.
OnLive is the gaming service that streams your game input and output over the internet. There's a little lag, but you can actually play modern PC games on machines that would have never dreamed of it.
The game streaming service announced that it has dropped plans for a monthly base fee to access the service. That means that anyone can join and play demos, spectate and interact with other members for free. Playing full games requires payment, of course.
No credit card is needed until the user chooses to purchase time to play.