I have a 6600 and the lead from the card should have a white connector with either pins or holes in it .
Anyway...... All you need to do is find one of those sockets that is hanging free that has corresponding leads in it and is the opposite fit i.e. if the card is male then find a female.
Don't worry if there are more leads in the free socket so long as it has at least the corresponding ones i.e. if the card has a black and a red the opposite join has to have a black and red that will line up.
Sorry this is garbled, all holes, pins and cables but it's hard to describe .