One of the better resources on the Web to understanding NAT is http://www.cisco.com/warp/public/556/nat-cisco.shtml.
You can find a good troubleshooting document and a number of examples at http://www.cisco.com/en/US/tech/tk648/tk361/tk438/tech_protocol_home.html.
The two RFCs mentioned in this chapter appear at http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc1631.html and http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc1918.html.
One of the better resources on the Web to understanding NAT is http://www.cisco.com/warp/public/556/nat-cisco.shtml.