Hello, in older versions of mIRC, all the files were put in the same directory.
In the newer versions, mIRC, by default, use a special folder (Appdata), to make sure it can write to this directory (for example, if you were to install mIRC to program files folder, mIRC wouldn't be able to write to this directory on Windows 7).
You can force the old type of installation by installing to a directory containing a mirc.ini file (empty, or not).
Indeed, if you install mIRC twice with a default installation to the folder C:\A\ and C:\B, both mirc.ini and others settings file required for mIRC to work will be put in the Appdata folder.
There are severals ways to get different profiles, with different scripts and different settings.
You can use the mirc.ini method I mentioned above (which is what Froggie is talking about), but this means you have one mirc.exe per profile, which might not be desired.
The other method is to use a shortcut with the -r command line switch, to indicate mIRC what is the settings folder you want to use, this method is explained very clearly here: http://en.wikichip.org/wiki/mirc/virtual_profile
Your suggestion doesn't make sense, you can't indicate in mirc.ini what folder to use because mirc.ini would be contained in that folder, mIRC needs to know the folder before loading mirc.ini.