errrrrr,
not to be short or anything like that but when you first registered your copy of mirc you should of recieved an email with the registrar's name and acct number.
once you have this you can transfer your registration to the new computer by entering this information where it asks in the registration section of the app.
It's not automatic or anything like that, you have to do it manually
If you don't have that information handy then i'm sure you can contact someone at mirc and provide the correct information you used when you registered it and get it again.
FYI: It HAS TO BE entered EXACTLY as it shows in your registration or it won't work.
ahhh shoot...this is what i get for not paying attention lol
goto the link MTec provided
Laterz,