OBJECTIVES: I. Determine the maximum tolerated dose of capecitabine when administered in combination with paclitaxel and trastuzumab (Herceptin) in patients with metastatic breast cancer. II. Determine the response rate of these patients to this treatment regimen. III. Determine the median time to treatment failure in these patients with this treatment regimen. IV. Determine the incidence of cardiac toxicity in these patients with this treatment regimen. V. Assess the quality of life in these patients.