select max()

Hello,

I have this table where I store player results for each week:

# select * from pref_money limit 5;
id | money | yw
----------------+-------+---------
OK32378280203 | -27 | 2010-44
OK274037315447 | -56 | 2010-44
OK19644992852 | 8 | 2010-44
OK21807961329 | 114 | 2010-44
FB1845091917 | 774 | 2010-44
(5 rows)

I'm trying to find the winners for each week and
also how many times the player has won,
so that I can display a number of medals
at his or her profile page.

I'm trying:

# select id, money from pref_money where money in
(select max(money) from pref_money group by yw);
id | money
----------------+-------
DE8048 | 3927
VK91770810 | 6133
DE7115 | 6655
OK252342810632 | 8053
OK228530000997 | 1013
(5 rows)

But I'm worried that "where in" will return false positives
(for the cases with the same money values)
and also I don't know how to count the repeated winners?

Thank you
Alex