Actually, you should change the date format in BOTH criteria and report to YYYYMMDD. That way you will ensure a 'range match' by matching text fields.
In your report source query- add a column and 'arrange' the text in your 'date' field to YYYYMMDD.
On your report - create an invisible textbox and bind to this new query column.
In the OPEN REPORT code...
dim vd1 as string
dim vd2 as string
vd1 = format(me.date1,"YYYYMMDD")
vd2 = format(me.date2, "YYYYMMDD")
CRIT = "[YourInvisibleField]>=" & chr(34) & vd1 & chr(34) & " and [YourInvisibleField] <=" & chr(34) & vd2 & chr(34)
note: chr(34) = quotes - use these since you're comparing text fields.
Scott C