I will also suggest Peter Reinhart's book "The Bread Baker's Apprentice." It has detailed instructions for making and maintaining a sourdough starter, plus lots of great recipes for using it. I followed his instructions to make my starter - a wonderful success. :)
Sourdough starter is a yeast culture in a medium of flour and water. You have to feed it every so often to keep it alive, but you can keep it almost indefinitely. You can make it yourself using wild yeast by leaving a mixture of flour, water, and some sort of fruit like grapes that have yeast bloom on them (the white stuff that you can rub off with your finger) covered with a cloth on the counter for about a week, until it gets bubbly. Then remove the fruit and treat it like a normal starter. Amazon also has some options to order starter, but you also might want to check if there are any fermenting communities in your area, or if you know someone who can give you a little piece of theirs.
King Arthur Flour Company from Vermont sells it,yo. Their website also explains how to make your own.Many of their recipes start with homemade countertop poolish/starter. Give them a try...ch
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