 The study will consist of a Screening Visit; a Run-in Period approximately 2 weeks in duration; two 28-day Treatment Periods each with 4 clinic visits; a 4-week Washout Period between the Treatment Periods; and a Follow-up Visit. The total duration of the study for each subject will be approximately 16 weeks. DISKUS is a registered trademark of the GlaxoSmithKline group of companies. 