Winlogon.exe

I have a Windows 2000 system. As soon as I load Corporate Norton Antivirus 9.0 on, winlogon.exe keeps running in task manager and slowing the system down enough to make using it painful. As soon as I unload Norton Antivirus, it works fine again. I have 128 MB of memory, Nvidia GeForce video card. All Windows updates have been done. Any suggestions?