Add a secondary dataset to the report design that pulls the values from the lookup table. In the tablix, use the Lookup() function to find the value corresponding to whatever lookup ID is in the primary dataset. Reply back if you need more specifics. I can give you sample code if you provide (a) the primary key name from the lookup table dataset, (b) the foreign key name from the primary dataset, and (c) the plain text field name from the lookup table dataset.