IP Addressing and Subnetting (cisco)

Host and Subnet Quantities
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f33.shtml

IP Addressing and Subnetting for New Users
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml