Hi Marxs,
My first suggestion would be to avoid installing LabVIEW 5.1 if possible. This for a few reasons...
LabVIEW 5.1 has the option to install DAQ with LabVIEW. If you elected to install NI-DAQ with the LV 5.1 install, you will run into driver conflict problems.
If you want to use DAQms with LabVIEW 7.1, you will need to install NI-DAQ 7.1, 7.2 or 7.3. You can also use NI-DAQ 7.3 with LabVIEW 6.1. However, NI-DAQ 7.3 will NOT install support for LabVIEW 5.1. This means that you will not be able to use your DAQ devices in LV 5.1.
If you need DAQ for LV 5.1, you will need to go back to NI-DAQ 6.9.3. This version will work with 5.1 and 6.1, but you will loose functionality in LabVIEW 7.1.
My suggestions would be as follows:
-- uninstall LabVIEW 5.1 and all versions of DAQ that are on the machine
-- re-install LabVIEW 5.1 but choose the "custom" and elect NOT to install DAQ
-- Install NI-DAQ 7.3 and have support for 7.1 and 6.1 (no support for 5.1 is available)
Basically, when you try to mix these very old versions of LabVIEW and DAQ with the newer stuff you will run into driver conflicts that can be unpredictable.