Please help someone! re: ski simulator

Ive seen some cheap proski simulators on ebay, with some You Tube clips attached which makes them look ok.
Please has anyone used one, or another simulator for training. They seem to mimmic skiing action reasonably well.
I have one week skiing a year and I want to be ready for it! so please some feed back about simulators, are they worth it?
Info. urgently required, today! Please and Ta.