Speaking as a computer professional...there is no way that someone could use an e-mail virus to turn a computer processor into a grenade. Grenades are made of materials which are designed to fly apart and do damage (not to mention the explosive material itself); computer processors are not. We're talking about something that's about the size of a silver dollar here. In order to make something that small which could be rigged to blow up like a grenade, it would have to be made of materials which were designed to explode, and I don't think you could do that and have it work as an actual computer too.
Not that it'll stop these yahoos who are apparently so ignorant of basic technological facts that they buy into crap like this from spreading these things as rumors.