Table name as parameter in function

Hi,

struggling around with this for some time:

How can I use a table name as a parameter in a PL/pgSQL function ??

I tried this but it didn't work...

CREATE OR REPLACE FUNCTION my_row_count(text) RETURNS int4 AS '
DECLARE
num_rows int4;
BEGIN
num_rows := (select count(*) from $1);
RETURN num_rows;
END;
' LANGUAGE plpgsql;

Thnaks for any input!

regards,
alex.