Hi Daytona,
I would also think of using the current date and the RelativeDate function. Try this script and see if it works. It uses the first day of the current month.
String ls_date
Date ld_lastdate, ld_firstdate
//Get the first day of the current month - as a string
ls_date = String(Month(Today())) + "/01/" + String(Year(Today()))
//Get day before first day of this month
ld_lastdate = RelativeDate(Date(ls_date), -1)
//Get first day of last month
ld_firstdate = Date(String(Month(ld_lastdate)) + "/01/" + String(Year(ld_lastdate)))
It assumes a short date format "mm/dd/yyyy". Hope it works.
Kevats