You still didn't answer the question about Windows version (it is still somewhat relevant - especially to that WHY question).
The brief answer -
IIS 'may' have been enabled if something like Remote Management was recently used (or a variety of other MS tools that want to 'push' things onto the web). Have you installed anything like Visual Studio or Sharepoint Designer?
In the Windows Service Control Manager - you can make the start type for IIS 'manual', and as long as you are not using a Microsoft service that is dependent on it - there will not be a comflict with Apache. If you need to use IIS for something, you can simply Stop the Apache Server and manually start IIS in the Windows SCM.
much too much info:http://technet.microsoft.com/en-us/libr ... 4(EXCHG.65
Look In Windows Services -