Paul, until you stop trying to anticipate everything everyone tells you, you're not going to get anything working correctly. Turn off the thinking and just do what you're told and, just like everyone else who has had the problems you have, and has done what they were told, you'll be working.
Follow Riamus' instructions. Go to portforward, find your router, pick mIRC DCC and follow every single thing they tell you to do - including setting a static IP. Don't argue, don't try to figure out how to do it better, or even why they're telling you to do what they're telling you to do - just do it. Precisely and exactly.
If you do, it'll work. If it doesn't work, you didn't follow the instructions precisely enough.
Thousands of people have DCC working in mIRC through the same router you're using, with the same provider, so if you can't get yours working it's you, not mIRC, not your router and not Comcast. You had it working once, so there's nothing wrong with the equipment or the software, just the setup.
