How do I SELECT primary/foreign keys?

Hi all,

for an algo I need to select the primary key and foreign keys from all the
colums in a given table. Is there any SELECT that can do this for me? I'm
currently looking into the postgresql standard tables, but I still didn't
find my way out.

Any help GREATLY appreciated.
Wim

-- 
ffrt (pgp public key on simple request)
Key fingerprint: FE F8 D4 63 A5 93 98 80  AC 7F 95 C1 85 6E 39 53