date function questions...

Hi!

I'm try to implement some kind of comany database into postgres,
but unfortunatly I don't know the how to solve the following porblems:

- how to test is any date in the same month as we are, or
month '1999.10' for example?

- how to convert 'seconds' to 'hh:mm:ss' format?
(int) --> (time)
select time(5);
returns '01:00:05' am I triggered a bug?

anyway I'd like to write this kind of date/time functions, and I tried
too...
but without any success... could somebody send me some kind of examples
to handle date/datetime/time/timestamp from C function..
(or either plpgsql.)

Many thanks,
Redax