Hello,
The GPIB-232CT-A is basically a string repeater from one interface to another (depending on the mode it's in). Here are two great documents which should give you all the information you need:
1. Helpful Hints for Using the GPIB-232CT-A
http://zone.ni.com/devzone/conceptd.nsf/webmain/58763F72C7830BB786256804005D8B77?opendocument
2. Using a GPIB-232CT-A or a GPIB-485CT-A in G Mode
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/862567530005f09c862564df005a468a?OpenDocument
Repost if you are still having trouble!
Best Regards,
JLS