sandisland,
Whether you need signal conditioning can depend on many factors. Many situations involve needing excitation for a sensor or to amplify a voltage. If your voltage is already in the range of 0-5v then extra amplification will not provide much benefit. Signal conditioning can also provide filtering or Frequency to voltage conversions for you. The need for signal conditioning will depend on the signal and the measurements you intend to take form the data.
To view a list of the analog input signal conditions offered by NI, visit: http://sine.ni.com/apps/we/nioc.vp?cid=3002〈=US
Hope this helps.
Kevin R