Other comments here have shown how to set up and test the ENET-GPIB itself. Once you have that, you should go into MAX, right-click on Devices&Interfaces, and create a new GPIB-VXI interface. The Agilent GPIB-VXI controller address is usually primary 9, secondary 0 (that is different from None). You may have to exit MAX and restart it, just to be sure it got saved properly. Some older versions of NI-VISA don't rescan for GPIB-VXI controllers properly when you create a new one.
Also make sure your VXI logical addresses are multiples of 8. Sometimes the Agilent GPIB-VXI controllers have problems with register-based VXI instruments that are at other addresses.
Once you have all that set up, you should see the VXI devices under the GPIB-VXI controller. I a
m not sure, but your comments sound like you may have already gotten to this point and aren't sure how you did it.
The resource strings for these devices look like this: "GPIB-VXI::::INSTR". Run the NI-VISA Interactive Control utility and it should auto-detect the instruments. If MAX found the instruments, so should this program. You can use this to try accessing your instruments.
As to your final question, yes, NI-VISA should work just fine for you.
Dan Mondrik
National Instruments