Assume little computer familiarity or aptitude. Some stuff is obvious, like using only a few large icons for favorite Web sites, or an icon perhaps for composing email and another for checking email.
Seriously, people who don't have significant expertise, should not be using Windows connected to the Internet. Your senior citizen is pretty much guaranteed to lose, unless they either stay off the 'net or get some pretty intensive training.
Computer dorks don't normally think this training is necessary, because the idea that downloading and executing malware is a bad idea, seems like common sense. But the world has shown that it's not common sense. So if someone is going to be on the 'net and not get educated, they should be using a platform that doesn't go out of its way to be unsafe (e.g. downloaded files do not automatically have execute permission, etc). Even a 10-year-old Linux distribution is going to be more user-friendly.
So, to answer your question: configure Windows for a computer-newbie (someone who is both untrained and not legacy-app-bound) on the internet (you mentioned email and web), by uninstalling Windows. Some people are rolling their eyes and mumbling that this is a sarcastic "solution" but it's really not. This is the best and most cost-effective and most practical thing you can do.