Problem of Null Ordering

Hi all,
I got some problem with the ordering.
I have a table which have a integer field , namely IF1, which is able to
have NULL value.
When I query this table and Order by IF1, the row that have the value of
NULL will come after the row that have a number value. I am wondering is
there anything I can do to make the row with Null value come before the
row with a number value. (Same as other RDBMS does - Sybase, MYSQL etc.)
Be more specified, I want to do something in the DBMS level instead of
doing some union queries. And apply this standard to all other query and
table in PGSQL.
Thank In Advance.

Harry Yau ( ^_^ )