I have a PC monitor that I need to connect to my apple mac 10.4.10. I already have my cinema screen mac monitor connected but want to create a dual monitor environment (for editing on final cut pro)... there are two montior ports at the back... both slightly different.. the free port is slightly wider with circular ends!! Have been trying to track down an adapter but so far have had no luck!! Help !

What Mac are you using? It sounds like a Mini or Pro? Here is a list of the adapters Apple offers. With out the model this is as close as I can get

That is an Apple Display Connector. I guess this must be on a Mac G4. It has USB, video, and power all in one. Unfortunately it is not used on anything but a few old Apple monitors. There are adapters available for about $30 on EBay. But first, confirm that it will have a separate video signal from the other monitor. Check the specs at Apple.com for your Mac.