I use IBM's ViaVoice in conjunction with Corel's WordPerfect for dictation purposes, as that is my personal preference. I tried to get it to work with mIRC, but with no luck. I think it might be possible to get it to work with mIRC by having a script that uses COMs to relay the information between mIRC and ViaVoice. I don't know for sure, and my knowledge of COMs is limited to what is written in the mIRC help file.
As far as a quick & easy installation of speech recognition for the purposes of using mIRC, I don't see anything.
I haven't tried this, but Microsoft's Speech Recognition information and downloads are
here
