FTS question

I created a FTS index:
CREATE INDEX clients_fts ON clients USING gist( to_tsvector( 'english', name) )

I can do FTS queries like:
SELECT * FROM clients
WHERE to_tsvector('english',name) @@ to_tsquery( 'english','somestring');

But if I want to query just part of the string return set is empty:
SELECT * FROM clients
WHERE to_tsvector('english',name) @@ to_tsquery( 'english','somes');

returns no results.

Is it that postgresql doesn't support substring queries or have I missed something. I can not find anything on the net. Postgresql is v8.3.1.

by
TheR