The official viewpoint is, for the sake of saving a lot of complication, that you shouldn't. And in general that policy is one to keep to and a good bit of advice to give newbies who have a tendency to download mIRC packaged with scripts, which are sometimes packaged with a virus/backdoor and/or altered with a crack.
mirc.net however is a trustworthy website, and has permission from the author to redistribute mIRC in its unaltered form, and gives full credit to both Khaled and Krejt for their contributions - mIRC and the FAQ respectively.
You wanted a place to download old versions of mIRC. I gave you a place. Sorted?
Regards,
