Thread: Having only one function run at higher priority

yes it will...
but I prefer to make one-shot settings to the next event based on timeprocessing for previous event, because in my code MM events do not occure with equal intervals...

Please tell me that neither MoveObjects, nor ProcessInput, nor anything else in that loop in AdvanceClock does any drawing, or other operation that might take so much as a millisecond?
If either of those do, then that would be your problem. You need to decouple your fixed rate logic updating, from your frame rate. If your logic update rate is 60fps but your PC can't manage to draw as fast as 60fps (possibly due to other programs using CPU) then you will get the problem you mention.

timeGetTime should really only be called ONCE at the start of that function, and everything else should simply be code that decides on how many logic steps to execute, or how long to sleep. The fact that you're calling it in a loop suggests you expect some things in that loop to take a little while, which as per the above, would be bad.

Make (1000.0/60.0) a named constant instead of hard coding 16.666...

I think another problem comes from the fact that you're asuming that AdvanceClock is called exactly 60 times per second. (Due to the Actual += 16.66666666666667; line near the start). However you then assume it isn't being called 60 times per second shown by that fact that you go on to compenstate for having slipped behind by adding Actual += 16.66666666666667; in the loop later on.
You can't do both! You can either rely on AdvanceClock being called exactly 60 times per second in which case you wont need this code to contain loops, or you allow it to be variable, in which case you need to remove the first occurrence of Actual += 16.66666666666667;
So, which is it?