i am well aware there are other posts on the subject, however my suggestion is a simplistic way of implimenting multi-threading(in a limited sense) to mIRC.
multi-threading should be based on a remote file basis, for instance, one .mrc would be on its own thread to another .mrc, so loading a 800 song playlist into a Media player wouldnt cause a MTS theme or mIRC itself to hang. and you could choose to bind as many script files together, for the purpose of keeping them in one collective thread.
finally, a flag for the alias prefix, like alias -l only it would be alias -t when that alias was called it would be called in a seperate thread, and would not cause the script to wait at all for it to finish.
thats my suggestion.