Is there any particular reason you're going w/ NI-DAQ 5.1?
Sub 5.1 was used for Windows 3.1.
Up to 6.1 supports legacy boards (our old ISA friends).
I believe NI-DAQ 6.1 was included in all versions of LV 5.1, and will make all the appropiate functions available in LV.
See also:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/862567530005f09c86256747006796fe?OpenDocument
2006 Ultimate LabVIEW G-eek.