Are you just trying to do the find, or trying to enter two dates into fields and hit a "find between these" button?
For a find, simply enter find mode, type in 2/6/2009...3/13/2009 and hit enter.
For a find layout, it is not a calculation, but a script:
Have two global fields gStartdate and gEnddate
Have the button run a script like:
Enter Find mode
Setfield [ Date_Com_Closed ; gStartdate & "..." & gEndDate ]
You're running into a wall trying to calculate something...there is no calculation.
If you are trying to display related records in a portal based on a date range, that can also be done using some inequality operators in your relationship. Post back if that's what you need here.
I would like to the know the answer to "displaying related records baed on a date range". Currently I use a global date field to show my records by single day how can I expand to multiple days?