 NOTE: 17-AAG is administered on days 2 and 8 during course 2 for patients treated at non-maximum tolerated doses MTD dose-escalation portion and on day 8 only during course 1 for patients treated at the MTD expanded cohort.Cohorts of 3-6 patients receive escalating doses of 17-AAG and irinotecan until the MTD is determined. The MTD is defined as the dose preceding that at which 2 of 3 or 2 of 6 patients experience dose-limiting toxicity. An additional 12 patients are treated at the MTD. 