I just finished looking into this very same issue for one of our applications. We downloaded a 30 day trial of the Datadirect ODBC driver for AIX. Configured the driver on the UNIX end and then used Oracle heterogenous services to access the SQL Server database. This worked very well. However, the owners of the application decided not to go this route due to cost. The Data Direct ODBC driver is licensed by processor and this was a 6 processor UNIX server. When I talked to the vendor about the cost of the driver they did say they would try to match what Oracle charges for the SQL Server gateway product they sell. Bottom line: unless you are going to use the ODBC driver (a lot!) to offset the cost of a development effort to access the data another way, it’s hard to justify for me.