There are two types of ip address.
1.static ip
2.dynamic ip.
Static Ip-address:
Static Ip-address will not change if you refresh the modem or switch off and on the modem again.It's remains same.
Dynamic Ip-address:
Dynamic Ip-address will change whenever you refresh the modem a new ip allocated for you......
If you need your computer ip do the following instructions
For Windows xp
1.start->Run
2.cmd
3.Type ipconfig
4.press enter
You can find your external ip address using any one of the online site .Recently i checked my ip address using
ip-details.com