You need to Add it via mIRC options, ALT+O > Connect > Servers. Click on the button 'Add'. For help with filling in those details, click on the 'Help' button.
This is going by 6.16 options, I can't remember if anything's changed, I doubt it for that section - it's always recommended you use the latest version of mIRC, yes, even if it breaks a script.
Regards,
