Hello,
I think NI-DAQ 6.9.3 should do the job. You can get it from ftp://ftp.ni.com/support/daq/pc/ni-daq/6.9.3/ .
Get the files NIDAQ693.EXE and then the LV51Eng.EXE (assuming your system uses the english language). Extract both into the same directory and then run SETUP.EXE from there, selecting LABVIEW 5.1 support.
Hope this helps.