Opening:
In an area with more than one router, it is common for a Windows 2000 and XP system to drift off the desired router to another. This happens when the signal strengths are relatively close, or interference causes signal strength issues.

What's Happening?
Microsoft intruduced a service component into Windows 2000 and XP. It is called, "Wireless Zero Configuration," in XP. It has a slightly different name in 2000. But, the service name is the same in both -- WZCSVC. This service constantly polls for the "best quality" signal of the ones being recieved. And, it switches to whichver signal is the best quality.

Is This A Problem?
Yes, in today's environment. These days, wireless encryption protocols are common place. Chances of two wireless routers having the same encryption codes are only probable when they are used in their default configurations (no user intervention). The things that could happen include:
- Loss of Internet - If the intended router has an encryption scheme, then switching from the desired router is going to cause loss of connectivity to the Internet. But, it will be intermittent as the service switches between the discovered routers. If the workstation connects to another resource (server, printer, shared directory) with the desired router, that resource will also become intermittant.
- Nothing - If the routers are the same, or don't have any user-invoked security settings, then Internet activity may not be lost. But, any network resources on the desired router will not be available while utilizing the outher routers.
- Security Breach - If another router is running tracking software, it is possible that user data could be logged. This is especially true if no encryption is being used.

Can I Stop This From Happening?
Yes. And, it won't cause issues with your current connection. Windows always remembers the "Last Known Good Connection" for network related devices. So, it will try the same one each time it starts.
- Right-click on the My Computer icon, and select Manage from the pop up menu
- Expand the Services and Applications item
- Select Services
- Scroll down the right side to Wireless Zero Configuration and double-click to open
- Set the Startup type to Manual, and stop the service
- Close the dialog boxes

Are There Any Drawbacks?
Moving to a different router, intentionally, will then set that state to the new router. So, it will be necessary to manually switch router connections for mobile users.

NOTE:
Remember that wireless signals are transmitted through the air, and can be intercepted. Not using an encryption method will always leave data in a readable format, if intercepted.