Where exactly is gta-vc.exe located? Normally its in 'C:\Program Files\Rockstar Games\Grand Theft Auto Vice City'

Looks to me that your pointing VC-MP to the disk and not the directory. Point it to where the EXE is and it should work fine.

When it asks to locate it, just select the directory since the exe wont show up (if i'm remembering the selection right) so if its in the normal place, select the 'Grand Theft Auto Vice City' folder