IF function HELP

Ok I would like the if function to reply with "0" if the criteria is not met, but then reply with another function if the criteria is met. Simular to something like this...

=IF(F3 <>0,"=Sum(F2:F3)",0)

The only down side is that it wont insert the additional function, only the text of the function. Is there any way to work around this? Any ideas would be greatly appreciated... I'm going crazy over it.