use this for your ole query
SELECT C1, C2, C3 from T1 where C3 >= ?
then click the parameters button and map your [User::MyVar] to the parameter.
any time you use a ? it creates a place holder in the parameters section which you can map to variables. Now this is not always supported by the OLE provider, pervasive OLE for instance does not.
Also the order in which the ? appear in the SQL statement is the order that the placeholders show up the params section.