How can I get the Db Schema Info??

Hi,

I have a query regarding the SCHEMA INFORMATION.
I require following information about a database i.e
1)How many tables are there?
2)What are their names?
3)What are the column types in each of the tables?
4)Primary key and foreign key information about a specific table.

This information is available by running commands like \d <table name>,
but what if
I want to execute a query to get this information.
i.e. I need the result in the recordset format for which I am require to
execute the query.
So, are there any sysobjects, System tables which stores the catalog
information?
Pg_tables is one but what about the column info (data types and all).

For e.g.:
select * from pg_tables where schemaname = 'public';
Gives all the user tables but I need the complete picture.

Thanks in advance,

Rajan Bhide