I like the Mac Mini, it is very affordable and you can keep using your existing monitor etc.
Although at home I have a cheap clone PC that does its job ( I work in IT and take the parts of the shelf at work).
The problem with all consumer AV products is that they try to get too much features in which you dont need which in turn slows down your new PC.

If it is just AV you want there are plenty of free and good alternatives, I kinda like this one:
AVM.com

You should probably wait till Windows 7 gets released in Q4 though, it really is a lot better then Vista (been using it for nearly a year now).

About McAfee: The consumer version sucks, the Enterprise one is really good though.