how do i get months out of start and end date?

hi guys i am a bit weak in asp.net so please suggest me something which 
can fix in my shoes.
now i had a requirement to get days out of start and end date which i got by the following code:
TimeSpan days;
days = Convert.ToDateTime(txtenddate.Text) -  Convert.ToDateTime(txtstartdate.Text);
txtduration.Text = days.TotalDays.ToString();


now here both start and end date are validated by the compare validator.
now i need something which can get months in digits like 4,5, or 12 or may be in words like
january, feb etc.
not only that but when the months are selected in a dropdownlist it should show
the number of days in that month.


guys actually i am trying to make here a monthly installment program work
if  u guys have any thing better than this please explain me
thanks



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