The easiest way in Windows to create a GUID is by calling CoCreateGuid in OLE32.dll. However, you need to pass a structure to this function. LabView's Call Library Function can't pass structures. You may create a simple DLL wrapper in C/C++ or VB which takes longs and a byte from LabView, builds the structure and calls CoCreateGuid.
Look at these links which show VB examples using CoCreateGuid.
http://www.desertware.com/vbuniverse/createguid.html
http://support.microsoft.com/default.aspx?scid=KB;EN-US;q176790&
Or look at this for a detailed (!) description of the algorithm.
http://www.webdav.org/specs/draft-leach-uuids-guids-01.txt
