Making Yogurt, part 1

I am on doctor's orders to eat yogurt every day.  Well actually, she told me to eat yogurt three times a day, but I just can't consume that much yogurt.  She recommended that I try to make my own yogurt because it's easier, cheaper, and tastes better than store bought.  I bought some freeze dried yogurt starters, and I finally got around to trying it out.

My first attempt was a total failure.  What I ended up with was essentially stinky milk.  Why didn't it congeal?  You are supposed to heat up the milk to the boiling point and let it cool to 108 degrees.  Then you add the packet of bacteria and let it incubate for four hours. 

I think this is where I failed, "incubate".  Am I supposed to have some sort of yogurt machine that keeps the milk warm while it is incubating?  Great, one more appliance to clutter up my cupboard.

What do you all think?  Have you tried this before?  What am I missing?  Your advice is much appreciated.