Top n queries and GROUP BY

All,
This is a straight SQL question, maybe not appropriate for a performance
list, but...

I have a simple stock holdings setup:

=> select * from t1;
nam | co | num
-----+-----------+------
joe | ibm | 600
abe | ibm | 1500
joe | cisco | 1200
abe | cisco | 800
joe | novell | 500
joe | microsoft | 200

What I would like to see is a Top-n-holdings-by-name", e.g, for n=2:

nam | co | num
----------+--------+-----
joe | cisco | 1200
joe | ibm | 600
abe | ibm | 1500
abe | cisco | 800

I can get part of the way by using a LIMIT clause in a subquery, e.g,

=> select 'abe', a.co, a.num from (select co, num from t1 where
nam='abe' order by num desc limit 2) as a;
?column? | co | num
----------+-------+------
abe | ibm | 1500
abe | cisco | 800

but I can't figure out a correlated subquery (or GROUP BY arrangement or
anything else) that will cycle through the names. I vaguely remember
that these kinds or queries are hard to do in standard SQL, but I was
hoping that PG, with its extensions...

Thanks, Rich Cullingford
rculling(at)sysd(dot)com