Find Begining and end dates of the previous month

[PNorm]

Hello,
I am looking for the formula to find the beginning and end of the previous month. If today is march 28 th then I would like to find february's beginning and end date using the system date.

When my crystal report runs it will find invoices, from the previous month.

Post_date between (beginning of February) and {End of February}.

Post_date is formated as MM/DD/YYYY HH:MM:SS am/pm on the db. I want to check against "MM/DD/YYYY"

Thank you,
Pn