Collision, Network Card.

I am having a lot of collision with a network cards. The computers are just peer to peer. The cable is fiber optic and OS is Win2k and ram on both computers are 512. What could be the cause of the collisions and how could I clear it up? On a 10/100 network I know how to clear this issue up but with a peer to peer I can not get it to clear up. Any suggestions?