First of all a steam cleaner will not make a good carpet cleaning machine, have a look at the carpet cleaning section for advice on a half decent machine.
In my experience steam cleaners are a pain, I had one that cost £1500 a few years ago and it was very disappointing, but saying that I could do with one now as I have a big clean up to do and the customer had asked for steam cleaning, to hire one is £40 a day.
I thought an industrial steam cleaner was going to blast away every bit of dirt I could find, but they don't

. I know some people on here get on well with them, I didn't, also found with the amount of steam created it was difficult to even see what you are doing and where you are aiming.