Windows 7 - How can I run HALO 2 Vista on Windows 7 Home Premium

 When I try to run HALO 2 that requires Windows Vista to run on. I didn't think that My machine that is running Windows 7 Home Premium would be a problem,   However I get a message telling me that it can't run it because I'm already running it in the background.   I have no idea why this is happening because I certainly haven't tried to open or run it,

Go to the task manager in windows and see if the process is running.  If it is, then right click it and kill it.

The install "may" have put something in the start of your computer.  Use the "run" command in your windows start menu to launch "msconfig".  You can see what is set to start up when your computer boots.