calculate date

[Newbie]

Hi,

I have a datepicker that gives a date - when I use the date entered I want
it to convert the dateto control value to the month end date of the month
selected (mdateto) and then mdatefrom is to be calculated using the mdateto,
mdatefrom = 12 months prior to the mdateto value

eg1
dateto control = '17/12/2003' ...... mdateto = 31/12/2003

mdatefrom = 1/1/2003

eg 2
dateto control = '4/4/2003' ....... mdateto = 30/4/2003

mdatefrom = 1/5/2002