problems playing with dates from any month.

[krishnakant Mane]

hello,
I have a very strange problem and I can't find any solution for that.
I am working on an accounting package which I wish to develop in python.
the simple problem is that I want to knoe how I can know if the given
date is the nth day of a month.
for example if a customer is supposed to pay his installment on every
5th of all months,
I want to know if today is the fifth day (jan the fifth, feb the fifth
etc) for any given month.
I have not found any such function.
if I have looked (or over looked ) in the wrong places I am really sorry.
secondly I also want to know the way in which I can convert a given
string to a date object.
for example if I have a string "29/09/2005", I know it is a valid date
although it is in a string form.
now I want to convert the above string into a real date object.
how can I cast it this way?
regards,
Krishnakant.