Yong--
Dennis is right on...1.2 is the minimum version of VISA that you need, so anything later than that will work just fine. If you have LabVIEW then you already have VISA on the accompanying driver CD. Once you find that, if it is less than v 1.2 then simply go to the website (
www.ni.com) and download an upgrade to the latest version. If you do have LabVIEW and a serial number, but are missing this driver or driver CD, call a sales rep. (referenced below) and they can help you get that driver.
I just wanted to add that if you don't have LabVIEW, maybe you wanted to use your instrument with VB or C++, then you will need to purchase NI-VISA for a small fee. You can do this by contacting a sales represenative at (888) 280-7645 or Fax: 512-683-8411 and they can talk about pricing and send you a no-obligations quote.
Hope that helps.
John H.
Applications Engineer
National Instruments
http://www.ni.com/support