Capecitabine was approved by the FDA in 1998 for treating metastatic breast cancer. Capecitabine is a pill that blocks the way cancer cells multiply and grow. Usually, this medicine is taken twice a day for fourteen days. Then, patients do not take the pill for seven days. With this schedule and dose, some patients have had side effects that interfered with their comfort. We have used mathematical models to recommend a new schedule of capecitabine. In animals, 7 days of treatment with capecitabine followed by a 7-day break was safer and more active against breast cancer. The purpose of this study is to find out what effect (both good and bad) capecitabine has on you and your breast cancer when given in this new schedule and combined with lapatinib.