If you are assigned to Phase II, you will be randomly assigned (as in the toss of a coin) to one of two treatment groups. Participants in one group will receive treatment with paclitaxel only (every 21 days). Participants in the second group will receive treatment with paclitaxel (every 21 days) along with imatinib mesylate (every day). The dose level of imatinib mesylate that you receive will be the same as the dose used during Phase I. The computer-generated assignment will favor the treatment group which is more effective. For example, if the combination of paclitaxel and imatinib mesylate is more effective than paclitaxel alone, then more patients will be selected to receive the combination therapy.