headsethair.
Have a look at
http://www.usbusiness.com/helicopter/sim01.htm
The contraption you saw may have been the Augusto SVH3 training helicopter. a google search will bring up loads of information.
They have one of these trainers at Bankstown airport here in Australia. CASA will allow you to credit up to 10 hours on this trainer towards your PPL(H). Not sure about the CAA's or FAA's position.
Basically the helicopter (a single seater, piston engined, two bladed, semi rigid rotor) is as you describe attached to a "trolley" and you can bring it up to the hover, do turns and fly forwards/backwards etc within the confines of a perimeter. The instuctor has a hand held contol unit where they can control those vitally important things like engine power available and rotor rpm and I suspect do their very best to keep you working hard!!!!
Hope this info is of interest to you.
Fly Safe.
heli_spy
for the record I haven't personally had a go on one of these trainers