Patients receive trastuzumab (Herceptin) IV over 90 minutes on days 1, 8, 15, and 22 plus oral R115777 twice daily for 3 weeks. Treatment continues every 28 days in the absence of disease progression or unacceptable toxicity. Cohorts of 3-6 patients receive escalating doses of R115777 until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose at which no more than 1 of 6 patients experiences dose limiting toxicities.