Check out Dom's Beginners Page for invaluable help on getting started with Sourdough. A series of 5 basic tutorials on sourdough baking. The tutorials are:
How to make your own starter.
How to use short kneads to handle moist doughs and bake a loaf with a yeast-based preferment.
The subtleties of proving a loaf using a ‘biga’.
How to shape a loaf using a hybrid recipe.
The final crucial steps and putting it all together to bake a 100% sourdough loaf.