It can be done, but not via the GPU card. You'd need to buy a capture card with HDMI input. Cheapest decent one I could find was $125. Obviously it's not a practical solution unless you're doing game videos/reviews.
What you really need is one of these...
http://www.monoprice.com/products/pr...seq=1&format=2
Or one of these...
http://www.monoprice.com/products/pr...seq=1&format=2
That will allow you to hook up your PS3 directly to your monitor without going through the PC. Far cheaper than a capture card and you'll get better results. Only downside is you'll need to hook the PS3 up to external stereo speakers. You'll need something like this if you don't have a stereo receiver.
http://www.monoprice.com/products/pr...seq=1&format=2
You may also need this if your speakers have fixed wiring.
http://www.monoprice.com/products/pr...seq=1&format=2
You can plug it directly into your PC speakers. You just sacrifice surround sound. If you have an external AV surround receiver, you can alternatively use a TOSLINK optical cable.