Calling PL/SQL procedure from VB

[Raminder]

I have a question concerning VB with Oracle.
How do we call PL/SQL procedures having IN & OUT Variables from VB?
For example, I make a simple PL/SQL procedure:

CREATE OR REPLACE PROCEDURE PROCTEST(A IN NUMBER, B OUT NUMBER)
IS
BEGIN
B:=A*A;
END;

Now I try to call it from VB:

Private Sub Command1_Click()
Dim x As Integer
con.Execute ("BEGIN PROCTEST (2, " + x + ");END;")
Text1.Text = x
End Sub

I get a runtime error : Type Mismatch. How do I go ahead?
Do I necessarily have to use OO4O or use Global temporary tables to keep the OUT values and then transfer to VB?