Ted,
If you grab a copy of NI's File Manager (Tool>>VI Library Manager (File Manager.vi), and check through the code, they have something there for acting on double clicks. It works very well, and I was able to modify this tool for my own use to allow a VI to be loaded and opened from this tool.
Check out the code. You will have to do a bit of digging, but it's there.
Also, don't let anyone try to talk you into using WinAPI. That's poor form in my opinion. Stay within LabVIEW. One of these days, when a new operating system comes out (mine?), you'll be glad you stayed plartform independent.
Hope this helps.
Good luck