SAS/STAT 14.1 which runs on SAS 9.4 introduced the HPSPLIT procedure which builds tree-based statistical models for classification and regression, so you might want to check into getting a machine that can run SAS 9.4.
There is no procedure for building decision trees in SAS 9.1 other SAS Enterprise Miner. The TREE procedure that is available in SAS/STAT produces a tree diagram, also known as a dendrogram or phenogram, from a data set created by the CLUSTER or VARCLUS procedure that contains the results of hierarchical clustering as a tree structure, but this is a visualization tool rather than a tree-based statistical model.
Hope this helps!
Doug