I'm not a big fan of the "I'm a PC" stuff. The little kids are cute and all and the celebrities help ensure that people watch the spots instead of fast-forward them, but they still feel a bit strange to me. I think it's probably due to the fact that they are referring to Apple without actually doing so.
As the market leader in software this always felt a bit weird (sort of like Coke calling out Pepsi in a $300 million dollar campaign). You're already doing well, why make consumers think about another campaign?
Anyways...here's a video for Microsoft that I like. I have no idea what the link is for (assuming MS Office) but check it out:
Thanks to Scott for the link!