Determine data type of columns

I have a general purpose utilty for entering data into web based forms.  The
function that parses the data and inserts the record into a table is largely
unaware of the structure of the table it is operating on.  I am currenly
having problems with integer fields.  If I blindly quote all fields the back
end will complain about casting on integer fields.  Also I would like to do
some primitive field validation based on type before submitting to the back
end.

This brings me to my question.  The PQftype function returns an OID but I
don't see any documentation on how to interpret it.  Are the values constant
for the built in types (specifically int4, text, and date)?
Do I have to execute another query to determine the actual type?
Is there a way to encode the values in an insert/update statement such that
they will be quietly converted to the proper type on the backend?

I am using 6.3.2 but will be upgrading to 6.4 shortly.  Will that make this
any easier?

Bryan White
ArcaMax Inc.
Yorktown VA
www.arcamax.com