My script does the same as the short one someone else posted above, except it has more features. It just runs any time you click a link and forces it to open using the program you select. I'm not sure why it isn't working for you. I just loaded it up and it prompted me to select a file and I selected chrome. Then it opened links in chrome.
If you're trying it on that old mirc it might not work, I've never used a version that old so the script might not be compatible.
