Date Headache

Guys
I have a table 1 row, a start and end date of a period

create table xperiod(startdate datetime , enddate datetime)
insert xperiod (startdate , enddate)
values ('2004-04-01 00:00:00.000' , 2012-03-31 00:00:00.000)

I'm trying to retrieve a batch of 'smaller' periods from this where the relevant period is a number (of months) passed as a parameter (only ever 1, 3 or 6)


for example, if the parameter is 1 I will obtain the following rows each being a 1 month period starting at the xperiod.startdate value up to an end date of the xperiod.enddate value
startperiod endperiod
'2004-04-01 00:00:00.000' '2004-04-30 00:00:00.000'
'2004-05-01 00:00:00.000' '2004-05-31 00:00:00.000'
'2004-05-01 00:00:00.000' '2004-05-31 00:00:00.000'

and so on to
'2012-03-01 00:00:00.000' '2012-03-31 00:00:00.000'


if the parameter is 3 I will obtain the following rows each being a 3 month period starting at the xperiod.startdate value up to an end date of the xperiod.enddate value


startperiod endperiod
'2004-04-01 00:00:00.000' '2004-06-30 00:00:00.000'
'2004-07-01 00:00:00.000' '2004-09-30 00:00:00.000'
'2004-10-01 00:00:00.000' '2004-12-31 00:00:00.000'

and so on to
'2012-01-01 00:00:00.000' '2012-03-31 00:00:00.000'

Hope this makes sense !

I think I'll be ok on the logic for the while loop but my main problem is getting the endperiod value based on the startperiodvalue
Thx in advance