Are you talking in terms of...

http://www.bikeforums.net/bicycle-me...ble-guide.html

If so then as per that thread it is an aluminium rivet. Drill it out and find a friend with a rivet gun...

However have you tried wiggling things about? Sometimes I find a BB spindle does not wish to come out for the same reason until I wiggle it about. Sometimes it takes a lot of wiggling.