More recently, Microsoft have been running their own advert campaign. They did a set of adverts a few months ago which had various people saying "I'm a PC": the idea was apparently to show a wide demographic range, rather than "middle aged white guy in a suit". The current version is "I'm a PC, and Windows 7 was my idea!" Unfortunately, I really think that Microsoft missed the point, so these adverts are rather embarrassing to watch.
Going back to the Apple adverts, the key concept is "anthropomorphic personification" (like Death in the Discworld novels). So, when the PC guy starts sneezing, that represents a computer catching a computer virus. By contrast, the Microsoft adverts are all about people who use PCs, e.g. school teachers and SCUBA divers. That's fine, but then the tagline should be "I use a PC", not "I am a PC".
If you do want to stick with the original concept, this Shortpacked! strip did an excellent job. (You may need to read the blog posts here and here to understand the context.) Basically, there's a USB memory stick that doubles up as a Transformers toy: more specifically, Ravage, who is (sort of) a black panther. The USB stick comes with a software application, so that you can have a digital version running around on your desktop, but this only works on Windows. Following this through, it makes sense that the guy representing a PC would then have a robotic panther as a pet, giving him the advantage over Mac guy.
So, my advice to Microsoft: either embrace the metaphor, or avoid it altogether, but the current adverts just sound stupid.