Bread-Bakers v106.n038.4

I have a fairly good discussion about that on my web site at 
<http://www.sourdoughhome.com/convert.html> and a bit more information at
<http://www.sourdoughhome.com/convert2.html>.

My rule of thumb for a starting point is to substitute 1 cup of 
starter for a packet of yeast and to cut about 1/2 cup of water and 
3/4 cup of flour from the recipe, then adjust as needed.

Hope that helps,
Mike