The purpose of this study is to evaluate the effectiveness and safety of two antibiotics in the treatment of complicated urinary tract infection or acute pyelonephritis (kidney infection). A 5-day course of 750 milligrams of levofloxacin given intravenously and/or by mouth once daily will be compared to a 10-day course of 400 milligrams of ciprofloxacin given intravenously and/or 500 milligrams of ciprofloxacin given by mouth twice daily.