MMTask.tsk
(Microsoft)
Microsofts Multimedia Background Task Support Module. This is a hidden task in Windows 9x/ME which shows up only in the Processes List in Starter. MMTASK is a Microsoft background task which provides simulated multitasking for multimedia applications, so that, for example, you could be playing more than one AVI movie at the same time. This task does not exist in Windows NT4/2000/XP which are true multitasking operating systems.
Recommendation :
Leave it alone. If you experience error messages which mention MMTASK, and quite a few users do, then the problem is in most cases elsewhere, very often driver problems.