How to clean cloth upholstery (SP?)

[67ChevyRedneck]

I bought a 93 chevy seat from a board member and it is a really nice and comfy seat, but I can't get the danged thing clean. It's the 60/40 split bench and I've used a Hoover steam cleaner but it's not working too well. I think there is something wrong with the attachment part and the water is not hot (even with me filling the tank with hot water). I've cleaned the driverside 3 times and I thought I finally had it "looking clean" but when it dried I still had many "dingy spots." I know it will come clean because many really bad spots have come clean but I already have many hours into the drivers seat and the passenger side is just as dirty and almost twice as big. Would it be worth it to rent a steam cleaner? Maybe y'all can recommend a good cleaning agent? Has anyone had a seat cleaned by someone? About how much did they charge? This is a really nice seat, and I know it will come clean, I just don't think I have the right materials and equipment. Thanks guys.