mIRC introduced an addition to the IRC protocol with the /dccserver command, which allowed sends to go from the "server" to the client, but have the client initiate the communication. The receiver would then get the information, rather than having the sender push the information. By doing this, the responsibility for having more open ports fell on the receiver. The port normally specified for this was Port 59, which is one of the ports restricted by POSIX systems to privileged users. Because it is a bad idea to run normal applications as privileged users (for security and exploit purposes), it does not make sense to include this feature which primarily makes use of port 59.
NiH provides a separate application which is a command line interpretation of dccserver. The issue with lower port numbers still exists for this version, however this can be avoided using appropriate port forwards at the router, or granting port privileges to non-privileged users (which is not recommended).
There is also an available patch for intedgrating /dccserver with XChat. The code for this is based off of XChat 2.0.9, so it may or may not work (LifeIsPain hasn't tested it yet, and quite possibly never will).