Regarding the first comment. I find myself needing this feature today. I really don't think it is so difficult to implement.
Every user has his own set of environment variables when he logs in; you could simply implement an environment variable say;
MIRC = c:\documents and settings\etc....
And MIRC will look in that directory for all of its settings, reverting back to the default directory (c:\program files\mirc) if no environment override is found.
This is really simple to code and woud be very helpful to at least me and the OP. :P
John.