At my salon we use Cocoa Keratin System because it's gentler on hair and the follow-up shampoo and conditioner is free from sulfates which can really ruin hair and make the keratin treatment last less.

If your hair is as damaged as you say then you might want to take some time to repair it before diving into a heavy treatment. Use natural oils like coconut or argan oil (recommend Pro Naturals moroccan argan oil!). BUT if you have your heart set on a keratin treatment, although I recommend that you get it done by a professional stylist, here's an article that might be useful to you:

Brazilian Keratin Hair Treatment Instructions - Yahoo! Voices - voices.yahoo.com