This is a Phase I study, which means these trials are generally comparatively small and are used to determine toxicity and maximum dose. Currently, there are no "standard" treatments for Recurrent CNS Tumors. In this study, approximately 14 patients with Recurrent CNS Tumors will receive treatment with irinotecan, an intravenous drug, and thalidomide, a drug taken by mouth. Both have been approved by the Federal Food and Drug Administration as treatments for cancer, but they have not been tested together for brain cancer.