This article is from the RSC/UKSC Cricket FAQ, by Ganesh with numerous contributions by others.
The various rain rules (including Duckworth/Lewis 2001
Update) are at
That page also has a D/L FAQ
In addition, there is a nifty Windows application at
This is the "Rain Ruler", applying D/L. It also provides a
full "pars" table for the side batting second.