Help Please!

Does Windows have a limitation to Timers? I seemed to be experiencing problems. I am currently in the middle of a project, it''s a shoot-em up. I am trying to use the timers to set-off the alien attacks. Basically something like this:- If(TimerA->Timer(200)==true)LaunchA=true; Now, the starnge thing is, this is OK for the first wave of aliens, but as soon as another wave appears(at the same time) the timing seems to go alittle wrong. Animation frames begin to skip, the aliens are not consistantly apart, rogue aliens which belong to another set of aliens appear on the end of the waves. Maybe it''s my method of programming and they way I''m calling them in. I tried the same thing using the ''for'' loop to create a kind of timer and that workd OK. However, the ''for'' loop will be inconsistant as different machines will take different amount of time to execute the ''for'' loop. So any help will be appreciated. Thanks Indy Indsoft