Be careful getting under the car. I would use a sturdy set of ramps:
A set like these work well:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11704&item=2084195058

Wal-Mart, Kmart, and Auto Parts stores sell ramps. Ramps are easy to use because you donâ??t have to jack the car up. I would also put some blocks or Jack Stands under the car and some wedges under the rear wheels. I have heard of cars falling on people. That would be a slow and painful way to die.