VACUM

You need to find a vacuum line that has a constant vacuum. Look to see if you can find on coming off of the intake manifold. Be carefull not to remove one the will effect the performance of the motor. I personaly like to use the hose that goes to the PVC valve. Remove the valve and simply connect the gauge in place. The reading for a normal heathly engine should be a steady needle between 17 to 22.
Hope this helps. Backyardmechanic :o
PS A vacuum gauge is a excellent tool for troubleshooting engine problems but is not used to much by mechanics today.