This is a randomized (study drug assigned by chance), double-blind (neither the investigator or patient will know the identity of the assigned treatment) to compare the overall survival of patients with advanced pancreatic cancer after treatment with gemcitabine with and without tipifarnib (referred to as R115777). Gemcitabine is an approved chemotherapy agent administered intravenously (iv) (though a vein) for patients with advanced pancreatic cancer. R115777 is an orally (by mouth) administered investigational drug that is being tested in combination with gemcitabine for the treatment of patients with advanced pancreatic cancer. Patients will continue to receive treatment with gemcitabine and R115777 (or placebo) unless disease progression or unacceptable toxicity is observed. All patients in the study will be followed for study assessments and safety for up to the 5 years, the start of further treatment, or death (whichever comes first). R115777 (or matching placebo) 200 mg will be orally administered at intervals of approximately 12 hours daily throughout the study. Gemcitabine will be administered iv at a starting dose of 1000 mg/m2 every week for the first 7 weeks, followed by 1 week rest, and then every 3 out of 4 weeks thereafter. Treatment with gemcitabine and tipifarnib (or placebo) will continue for up to 5 years (or until the start of further treatment) in the absence of disease progression or unacceptable toxicity.