Depends on the program, and I have virtually no experience with mIRC. I use XChat; for that, in the list of networks, just add a new one. Then after creating an entry for "silcroadg3c3mtu6.onion/6667", in the settings for that network just put in the proxy info. And make very sure "bypass proxy" is NOT checked, and "use global credentials" is NOT checked. You want a unique handle for the chat so it's more anonymous, and using the same one as you globally use less than unique.I'm sure it's the same in mIRC, but I can't tell you where to go or anything -- hopefully somebody else'll help you out there. Good luck.