Visit
www.portforward.com that will explain everything you need to know and in the simplest language possible and they will have a tutorial specific to your routers interface. Fantastic website.
If your not connecting to many peers then you may need to adjust the max number of outbound connections your OS will allow you to connect to. There is a hack created by some guys who run
www.lvllord.de that will allow you manually edit your tcpip.sys. I wouldnt bother with this as if you dont know what your doing you can screw it up but if you want to have a go then go for it.