You can have them enter a date and your select statement can control the month from that.
If you want them to enter a start date you can use
datefield in {?dateparam} to dateadd('m',1,{?dateparam})
or back a month flip it
datefield in dateadd('m',-1,{?dateparam}) to {?dateparam}
or for the curernt month selected
datefield in dateserial(year({?dateparam}),month({?dateparam}),1) to dateserial dateserial(year({?dateparam}),month({?dateparam})+1,1-1)
This being said, if you can you are likely much better off using a stored proc with its own date parameter and doing the record selection at that level. It is a more efficient process and limits your data retrieval better.
HTH