On a fresh install of mIRC the default mIRC font is FixedSys. mIRC doesn't 'pull' the default font information from anywhere. If your FixedSys font is different than everyone else's FixedSys, then it will obviously display differently. If your installation of mIRC isn't actually fresh, then your font could be different than the default.
Download mIRC from the Download link above, then install mIRC to a new (never used before) folder (uncheck all the "maintain options" checkboxes in the installer), and then use notepad to create a blank mirc.ini file in that folder. That will ensure you have a completely unchanged mIRC when you first run the new installation.
-genius_at_work
