People grow quite attached to their nicknames when they've been using them on the same IRC network for years and years. Naturally, they care about keeping that, and adding a '2' or a hyphen on to the end of your nickname just doesn't cut it.
AB3, there is little you can do if you don't use a network that has services such as NickServ to keep your nickname. On most other IRC networks only usernames (or nothing) is able to be registered, so nicknames are up for grabs.
I've removed some info from your post so others cannot take advantage of such a "service". Also be aware it hasn't got anything to do with mIRC, just another lamer that we have to put up with

Regards,