This work was supported in part by NSF Institutional Infrastructure grant no. CDA-94-01142, ONR research grant no. N00014-92-J-1801 (in conjunction with the ARPA Research in Information Science and Technology -- High Performance Computing, Software Science and Technology program, ARPA Order no. 8930), and Brazilian CAPES and NUTES/UFRJ fellowships. We would also like to thank Jack Veenstra for his help and support with this work.