Hi Miss I,
Yep a number of them have Power Plates or 3G Cardio 6.0s, you have to call around to find one. Likely the better equipped gyms will be the most likely.
Some charge a little extra to use them but usually they are reasonable fees. In the UK if you are still there also you will find some training gyms and studios that offer them.
For those of you in the Denver area, you can go try out the 3G Cardio 5.0 and 6.0 models and likely the Power Plate line up too at Colorado Home Fitness in Lakewood, Denver and Park Meadows.
Make sure you bend your knees slightly when you first get on them so it doesn't scramble your brains :-). Jsut kidding but it will feel weird and not so comfortable if you straighten and lock your knees with on them at a strong frequency.
You'll quickly get the hang of it and there are hundreds of positions and exercises you can do while on them that get a major boost in effectiveness.
Also women LOVE these machine not only for the much quicker way to get a solid full body workout, but its also one of the few methods to reliably minimize cellulite that really works as well!
My wife is a Skilled Tango dancer and swears by it for improving balance and coordination as well as keeping toned and fit in short workouts every other day while using it for stretching and massage on alternate days.