> could someone help me with the syntax on how to call a stored procedure
> in a stored procedure (I hope it's possible).

Executable stored procedure:
EXECUTE PROCEDURE proc_name [param [, param ...]] RETURNING_VALUES [:var [, :var ...]];

Selectable stored procedure:
FOR SELECT col, ... FROM proc_name(param, ...) INTO :var, ... DO ...

Ivan
http://www.volny.cz/iprenosil/interbase/