Well, I am cursed with the same problem as many other people. At the beginning of my arduous technical journey I knew nothing about configuring routers, forwarding IPs, and all that jive -- and now, well, I still don't know very much, but I've done a heck of a lot to try and resolve this problem!
-D-Link 624 router
-WinXP on SP2
With the help of a trusted technical advisor (a.k.a my best friend), I tried to address the DCC send/chat issue through the following methods.
-We cleared the locahost info as specified at the beginning of this thread in mIRC
-We set the ports to 5001-5005 in the connect advanced options
-These ports as well as 1024-1025 and 6060 were forwarded and allowed in the router's configuration
-Ident port 133 was also forwarded/allowed
None of the above worked, so we set a DMZ for my machine, essentially bypassing the router's firewall. That failed. We then disabled the windows firewall and my virus scanner, that failed to produce any positive results as well. I'm not behind any additional firewalls or proxy servers. I am able to receive files over IRC and receive a DCC chat, but not send files or send a DCC chat. My DCC works fine on my PC, the one that is directly connected to the internet, but my laptop that receives its connection from the wireless router is suffering DCC problems.
I have only one question left: what the frilly heck is going on? Is it SP2, the router (which I heard is flawed in some way), or mIRC itself? All of the above? I'm really lost at this point.