OP, For simple oil changes and such consider getting yourself Race Ramp "Roll-Ups" (Item RR-RU) as sold from this very good vendor..
Low Profile Ramps & Wheel Cribs
With the use of Roll-Ups either for use with the front or rear of your Z you will without problem, easily get your Z, 4" off the ground. With just that you can get under there and do an oil change on your Z. Now, if you find a real need to use your floor jack the Roll-Ups will get your Z up 4" and you will now be able to use your floor jack and one of the pinch rail lift points or at the front or rear lift point. Buy a pinch rail adapter for your floor jack as shown here for use when lifting at pinch rail sites ..
Floor Jack Saddle - Rocker Panel Pinch Weld Adapter New : eBay Motors (item 250588286969 end time May-28-10 13:53:50 PDT)
Reality is many guys, especially the inexperienced get themselves in lots of trouble using jack stands. Trouble like personal injury and or damage to the vehicle. BEST BET is to avoid jack stands for such little jobs like an oil change.