So, I don't recommend this. In fact, given that Microsoft has basically killed off OneCare, I recommend that anyone still using it move over to something else as soon as possible. So with the understanding that I will not, in fact, even try to see if this works, I know there are some out there who actually want this information.

I will pray for you. :)

So, I was testing Windows 7 but really missed OneCare and decided to try to install it. The trick is to make it think you’re using Vista. The problem is that the installer really has a bunch of mini installers so you have to make them all think they’re running on Vista. Also you have to make the main service think it’s running on Vista.

Thanks to Jorg S. for the link.