|Changes in your external IP address are up to your ISP (internet service providor). This is the IP address the WAN (internet) sees you as having. |
I believe you will need to speak to your ISP to prevent this changing.
I get the feeling you want to reserve a specific IP address on you internal network... So it always shows the same address in XP.?
Reserving a specific IP address on your internal network can be achieved by creating a "Static IP address".
A good place to start is www.portforward.com there are excellent tutorials, in particular about creating a static IP address.