>I display a form on top of my main form when a timer on the main form fires. How can I stop the timer from firing when that second form is on top?


You can either disable the timer, yourTimer.Enabled=.F. in secondForm.Activate() and re-enable it in its .DeActivate().

Or at the beginning of your method yourTimer.Timer() try something like:

If WonTop('secondForm')
   Return
Endif
&& your timer code follows

hth
-Stefan