Number Of 'Periods' In A Date Range

Guys
Date brain killer - I have a startdate and enddate and need, for a given period length in months, to identify the number
of periods betwen the startdate and enddate
so for example

DECLARE @Periods TABLE
(
StartDate datetime,
Enddate datetime,
NumberOfMonthsInPeriod INT ,
TotPeriodsINT
)

-- Initial data
insert @Periods
(
StartDate ,
Enddate ,
NumberOfMonthsInPeriod ,
TotPeriods-- for this illustration, initialised to 0 but need to be UPDATEd as per detail below
)

select
'30-Sep-2005',
'10-Apr-2009',
1 -- 1 month period
0
union all
select
'30-Sep-2005',
'10-Apr-2009',
3 -- 3 month period
0
union all
select
'30-Sep-2005',
'10-Apr-2009',
6 -- 6 month period
0

The following rules regarding periods apply
Each 1 (NumberOfMonthsInPeriod) month period is as would be expected ie
01-Jan - 31 Jan
01-Feb - 28-Feb (ie 1st March - 1 day which would deal with leap years - dateadd(...)
and so on to December

Each 3 (NumberOfMonthsInPeriod) month period is one of the following 'bands' per year
01-Jan - 31-Mar
01-Apr - 30-Jun
01-Jul - 30-Sep
01-Oct - 31-Dec

Each 6 (NumberOfMonthsInPeriod) month period is one of the following
01-Jan - 30-Jun
01-Jul - 31-Dec

I need to derive TotPeriods as follows:

For the row where NumberOfMonthsInPeriod = 1, the first period ie the one the start date falls within is 01-Sep-2005 to 30-Sep-2005, second is 01-Oct-2005 - 31-Oct-2005 and so on until
last period ie the one the end datye falls within is 01-Apr-2009 - 30-Apr-2009, a TotPeriods value of 44

For the row where NumberOfMonthsInPeriod = 3, first period is 01-Jul-2005 to 30-Sep-2005, second is 01-Oct-2005 - 31-Dec-2005 and so on until
last period is 01-Apr-2009 - 30-Jun-2009, a TotPeriods value of 16

For the row where NumberOfMonthsInPeriod = 6, first period is 01-Jul-2005 to 31-Dec-2005, second is 01-Jan-2006 - 30-Jun-2006 and so on until
last period is 01-Jan-2009 - 30-Jun-2009, a TotPeriods value of 8

Hope this is clear and thanks in advance