Try this page and email them. Technical Support query is what you need. You may also need to read any manuals that came with the router. All routers have a port forwarding feature (or port services) - that is, in part, the point of a router.

To set up mIRC's DCC ports, go to ALT+O > DCC > Options - the default is 1024 - 5000, but any two consecutive ports (i.e. 4441 - 4442) should work, provided those exact same ports are set up with the router.

You may also want to run a Search on these Forums for threads related to routers. Expand to 'All Forums' and 'All Posts' for best results.

I hope you get your DCC problems sorted out soon!