Block TCP port 6346 with Cisco 2610?

I am wanting to know exactly how to block specific TCP port traffic on my Cisco 2610. We use this to access the internet and people on the network have been using gnuetella and napster – now external limewire clients are scanning these ports and grabbing things without software running on a host machine (causing the network to really slow down). There may be multiple ports that I need to block. Please list the best ports to block (aside from 6346). If this is done with access-lists…please include a detailed example.