A great answer lies in a response to a similar question, posted by Greg McKaskle about five months ago:
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=506500000008000000B0140000&ECategory=LabVIEW.LabVIEW+General
In case the link doesn't work for any reason, the title of the initial question post was "finding default web browser". A search in the Developer Exchange or on the ni.com support site should bring it up.
I was able to open up a test HTML file on my Windows system using the argument (no quotes) "C:\windows\readme.htm" as the input URL.
By the way, System Exec will work, but it takes some playing sometimes and it isn't as bulletproof and platform-independent as the VI referenced in the post above. I was able to get my mac
hine to fire up the same test HTML file as above using this (no quotes) as an argument to System Exec:
"c:\program files\internet explorer\iexplore.exe c:\windows\readme.htm"
Regards,
John Lum
National Instruments