Connecting a PS3 / Xbox 360 to my iMac?

Hello,

I am new to this forum but have used the guides as iFixit before which are great. I am hoping to ask for a more in depth fix for the problem of trying to connect a PS3 / Xbox 360 to an 21.5" iMac.

While I am aware from previous forums that there are no adapters for the iMacs for the new release which allow you to connect your gaming console to your computer, I am curious as to whether there is the possibility of changing the graphics cards or other parts, in order to allow input from the mini display port.

Is this a possibility? If so, I'd love some advice on what sort of parts I should be looking, and the sort of costs I would be looking at.

Thanks