Select * from table where ((Field_A LIKE 'param') OR (Field_B LIKE 'param2'))
I'm going to assume LLBLGen 2.0 and C#.
IPredicateExpression filter = new PredicateExpression();
filter.Add(TableFields.FieldA % "param");
filter.AddWithOr(TableFields.FieldB % "param2");
If this doesn't work for creating the predicate expression please post the code that you are attempting along with your setup.