A lot of the Home Depot flooring associates I know and work with (I'm a sales rep for a carpet manufacturer) have positive things to say about the dry powder methods like Capture.
Chem Dry also had this cleaner in a can that looked like a miniature fire extinguisher; I heard good things about it but haven't seen it in stores in a while. You might get something like that from your local Chem Dry service, but that's really more for spot cleaning and not deep cleaning.
If you go with steam cleaning, just a caution -- loop pile carpet (like most berbers) will hold in the moisture more than a cut pile, and may take a bit more time and effort to completely extract. I've heard this from customers and from my employer's technical services department.