PART I (completed as of 09/06/06; all patients enrolled in study after 09/06/06 are enrolled in part II): Patients receive escalating doses of topotecan hydrochloride IV over 30 minutes on days 1 and 8 followed 6 hours later by bortezomib IV on days 1, 4, 8, and 11. Treatment repeats every 21 days for at least 4 courses in the absence of disease progression or unacceptable toxicity.