To have two clients running you install mIRC (To "Program Files" or "Program Files (x86)" if you run 64 bit windows)
Then use -r switch to start mIRC (Make shortcuts for easier access)
"C:\Program Files\mIRC\mirc.exe" -r"%APPDATA%\mIRC 1"
"C:\Program Files\mIRC\mirc.exe" -r"%APPDATA%\mIRC 2"
and so on... as many instances as you want to run.
(Of course I suppose you can use "My Documents" or whatever other location you have access to for storing the scripts and ini files)
So there isn't really a need to have more then one mIRC.exe

And yes I probably was exaggerating... still it felt kinda good to say it out loud again :P
As for the path issue I stand on my ground... IF application is programmed properly and is following windows programming guidelines it MUST work whether it encounters paths with spaces or not. If it doesn't then it's poor programming and should be fixed. Otherwise we could simply tear off the damn space key from the keyboard. Ifthespacescausesomuchtroublethenwhyusethematall?
Sorry had to say it once more. That's all from me about this topic.