Most settings are stored in the mirc.ini file, like the notify list.
Where this file is located depends ... well, my first try would be the installation folder, but maybe you're able to find it in your documents and settings folder -> your name -> application data.
About the invite thing, it's possible to ignore certain people for the case of invites only.
So you will still be able to see their text, ctcps, dccs, ... but invites will be ignored for you.
Take a look into /help /ignore
, the i switch should be what you're searching for.Edit:
Well, yes, this may be easier in the address book..