jonat if you cant send files, the problem surely lies at your end, when you initiate a dcc you are asking someone to connect to your PC with the designated port, if you are Absolutely sure your router is forwarding the correct ports, perhaps you are overlooking the inbuilt XP firewall
go to Network connections window, right click on the one you use > Properties > Advanced, uncheck the box that says Protect (IF) indeed it is checked,
Also if you send the wrong IP while trying to initiate a DCC the dcc will fail
A way to stop this happening (On newer versions of mIRC)
is once you log on to the Server type //localinfo -u this will fix any IP mismatch
ScoT
#mIRC Undernet
