well, what I could find on my googlin reckoned it was an s-video...
maybe if you could describe it...?
edit#1: ok, the abit website is reckons its a "TV-Out (S-Video/Composite)"
it also reckons you should have got an "S-Video/RCA adaptor", "S-Video Extended Cable" and a "Composite (RCA) Extended Cable" included in the box.
edit#2: or look here **broken link removed** and see if any of the connectors look like yours.
Tim
edit#3: whatever connector it is wil be widely available, but you will need to know what it is called first...