How can I play video game consoles on a PC Moniter?



I am looking for a good way to play my playstation using my PC moniter as the TV.
I have heard that TV tuner cards would work but there is a very noticable lag.
What would be perfect is a way to hook the console (coax or composit video) to the spare RGB input on my moniter.
Anyone know a way to do this? or a better way to put the video to my moniter?