set returning functions in v7.3

Hello,
I have a problem with "set returning functions".
I have a table t_groups. I would like to get the rows of it. I try to call
this function:

create or replace function getgroups() returns setof t_groups as '
  select * from t_groups;
' language 'sql';

in the this way:

select * from getgroups();

It should have returned with all the rows from t_groups. It did not. Where
is the problem?
If ther would be anybody who can help me I wuld be greatful.

Thank you very much.
Best regards, Csaba Egyud