DS-CDMA has been recognized as the major candidate for providing high and variable data rates in third generation wireless networks, where multi-code structures and different spreading gains will be employed. In this paper, we address the problem of assignment of variable spreading gain deterministic codes to a set of users, with the objective to maximize down-link system throughput. We propose an algorithm to allocate codes to users with different minimum rate requirements, based on code cross-correlation properties and spreading gains. Our algorithm first constructs an admissible set of codes by using criteria which are based on induced interference to the system and code rates. These codes are then appropriately assigned to users, so that user rate requirements are satisfied. Comparative numerical results for different performance measures of these criteria are also provided.