It's very straight to transfer data from SQLServer to Oracle
Step1:
Create a ODBC Connection (System DSN) for Oracle ODBC Driver

Step2:
In SQL Server open the IMPORT AND EXPORT DATA utility. You can do this directly as well as with ENTERPRISE MANAGER

-Choose a Data source with suitable Database name and type of authentication
-Choose a destination .IN THE DESTINATION DROP DOWN LIST PICKUP THE OTHER(ODBC DATA SOURCE) option
-Pickup the option to copy data from the source database
- Select the Tables you want to transfer the data

That's it....