The purpose of this study is to evaluate safety and efficacy of rituximab, with and without methotrexate, in joints, enthesium and skin in psoriatic arthritis patients with inadequate response to methotrexate who have either not tried anti-TNF therapy or have had inadequate or failed response to anti-TNF therapy. To explore biologic mechanism of action via histological and immunohistochemical evaluation of pre and post treatment biopsies of psoriatic plaques.