Two versions of 2600. Microsoft found a bug with version in which files are dated 8/18/01, and they fixed it in version in which files are dated 8/23/01, but both are still build 2600. If you don't know which version you have, go to C:\Windows and right click on explorer.exe (just an example file, _most_ other critical files will work too) and see what date was it created on.