ghoot, a completely different approach:

If you want to measure resistance of a photoresistor, why not use an RC circuit? No A/D or fancy chips required. Check out page 141 of the "Basic Analog and Digital" basic stamp document here:

http://www.parallax.com/dl/docs/books/edu/baad.pdf

It has exactly what you would like to do. Just change the syntax a touch to work with PBP.

Don