Your should first test your device's GPIB port to make sure it is activated.
Use IBIC
http://www.ni.com/support/gpib/max/ibic.htm/
If the ibln command returns true then it is on, if it returns false then you need to activate it manually.
This instrument does not respond to *IDN?, but you can send this command to reset and query the device in IBIC:
IN,SM0\r\n
For other commands, refer to your instrument's user manual or contact Agilent.
There is also an instrument driver for this instrument located here:
http://search.ni.com/query.html?lk=1&col=alldocs&nh=500&rf=3&ql=&pw=595&qp=%2BContentType%3AInstrumentDriver&qt=5334&layout=IDNet