i was wondering if this is possible in any way at all, even by converting maybe usb to hdmi or something.... at the back of the screen i have 2 firewire ports and 2 usb ports, thats it. Thanks.

That will NEVER work. Don't even think it.

The USB ports on an Apple Cinema Display are NOT for receiving video. They are merely a hub for USB devices.

Furthermore, the PS3's HDMI port will only work with monitors that are HDCP-compliant. The 30-inch Apple Cinema Display is NOT HDCP-compliant. You will NEVER get the PS3's HDMI port to work with that monitor.

You will need a scaler box to do this. Your resolution will be limited to 1280x720 (720p). Gefen are often the company used for such products. If you want to play HDCP content (can skip it for games using component out on the PS3, but it is needed for bluray) you need a product like HDfury. If you don't want to be switching things off and on to switch between using the display with different devices you will need a dual-link DVI switch.

In the end you can get an okay solution to play PS3 content on your 30" display, but it comes at a price. If you can find good deals then Scalers are $250-$300, an HDfury is over $100 and a switch is over $200 for a good quality 2-port model. Add in your cabling costs and value wise you are better off picking up a 32" HD TV if you have the space.

Depends on what connections u have on the other side. Sounds like usb to hdmi is ur best bet