You are either using NT 2K or XP
You should only
see an mmc.exe process if you are running a console created by it, like
services.msc (NT services), grpedit.msc (Group Policy Editor), devmgmt.msc
(Device Manager), and so on. If mmc.exe is in memory, you have a console
open (or it hung on close and got let in memory).
Have you installed any of the above snapins? bang the XP or 2K disk in the drive and type sfc /scannow into run...