You'll need to splice into the headlight connector. The simple way is to use a scotch type connector (available at any Radio Shack, etc.) Also, just find a metal surface to ground the gauges - if you have access to a multimeter, you can make sure you're grounded by probing the headlight connector with the positive lead and then touching the metal surface with the negative lead. If it shows voltage in the on position you're grounded.
**EDIT: Also, do a search for gauge install - there was a thread not too long ago that covered much of this I believe - it may be of some use.**