although i cant offer a solution to completing the instalation
i can let you know that it may not be nessicary, the neat thing about mirc is that as long as you have the mirc.exe program file, even on a system that mirc is not instaled on, mirc will do everything it needs to do when you run that file for the first time, from seting up registry setings, to generating files and folders in its home directory that are required for mirc to run

so as long as you have the mirc.exe program file extracted sucessfuly all you have to do is run it and mirc should work perfectly

Cobra^