The Network Addon Mod is a fantastic addition to SimCity 4. To install it, you first need to have Java. The Windows installer includes Java version 11, but it does not work on Windows XP.
After some trial and error, I found that this version can work on Windows XP and support NAM:
https://github.com/ojdkbuild/ojdkbuild/releases/tag/java-1.8.0-openjdk-1.8.0.332-1.b09