Simply: no, microsoft is not considering adopting WebKit for IE.
This appleinsider article, and others like it, took an out-of-context statement by Ballmer and stretched it into a farce.
I happen to live in Seattle and have friends who work on the IE team. IE8 sports a completely new rendering engine built in-house. It ain't webkit. My friends claim that when it is finished the new engine will render things, y'know, in a standards-compliant manner. Personally, I'm not holding my breath :-)