Well, I think you've already done it, but here's how I'd do that:
Your desktop's mIRC (already connected to an IRC server) will listen a port for remote connections and check for a basic authentification (like /quote id password). Then, it will transcribe everything it receives from the IRC server to this listening port (using the same IRC protocol), so any distant mIRC can connect to your desktop and simulate an IRC server (modes, channels, names, lists, etc...).
And you just have to create some customized commands to take "control" of your mIRC's desktop, like /quote msg #chan hello!
