parallel install uninstall

A year or so ago i had to install a parallel version of XP due to corrupt files. The installation was successful, the recovery was successful, and I merrily went on my computing way, happy that I recovered my system. Now that I’m housecleaning my pc, I see that I left the parallel installation in place. How can I tell which directory I’m loading from? And what exctly is the executable that starts XP nowadays?