Assess the efficacy and safety of ADA compared to ADA/MTX in patients with psoriasis. Many studies of ADA in rheumatoid and psoriatic arthritis have allowed patients on stable doses of MTX to continue on MTX while being treated with ADA. There has been no prospective trial of MTX and ADA concomitantly in psoriasis. Safety of ADA monotherapy vs. combination ADA/MTX will be compared.