if it's a socket 775 mobo/processor (which I think it may be) then try one of these - heatsink/fan combo's...
(posted a link to a low-profile one, as I didn't know how much spare room there was in your system case - the one linked below would probably be a better bet if there was room to fit it though!)
Edit: oh - and I'm sure you weren't actually trying to get around the "trading outside of classifieds" so please everyone, no more RTM's on this one...
yes its a skt 775 board.

Ps .... Hope I'm not breaking any rules ... If I knew the name of it ...then I could search for it .
Thanks
I had this CPU and board running for 3 years everyday without a problem .. I sold it at send it just as it was put together the day I bought it.
Not all boards have this part.
And if it was there and not meant to come off ... It would still be on it.
Well I have to say I just assembled an AMD Phenom x6 and it didnt have anything like this.
And as a 43 year old who has been building PCs on and off over the years I`ve never saw this until now.
Cpu was put in socket then the little lever was pulled back and secured to hold in place.
Then stick the heatsink/fan on.
Cheers