Considerations about the use of 64bit components:
Using the 64bit versions of Windows OS on application server allow the use of Java in 64bit mode and Apache Tomcat 64bit. This has the advantage that no limitation of the maximum memory pool of java processes will be needed.
64 Bit drivers for all components using Java and Tomcat processes will be needed. So e.g. database connections via a jdbc:odbc bridge using a System DSN will need a 64Bit driver for the database.