LoopyLoo has a good points - check your login script. Your "testing" sentence is easy to miss, so I'm going to assume you don't want time synchronized in your test environment.
Generally it's a good idea to synchronize time because this makes things sane. ...Even though, in our experience, Win2K is horrible at keeping it consistent - NT4 was worse - we use a hodgepodge of freeware instead.
To further an answer to your question, which LoopyLoo already gave a good response to, in windows 2000 services is a service called "Windows Time". I'm betting stopping this, and setting it to manual, will stop the timesync. Someone correct me if you know otherwise.