Tom's got a good point, Maddog. It's good practice to learn chord switching without any regard to rhythm. This gets you used to the mechanics without learning to walk and chew gum at the same time. Not only that, because you learn to switch more quickly without timing, imagine how swift and clean you will be when you are switching when you are going for timing.
After that, just take a basic strum, like the first one you'll find in the lesson
Much Ado About Rhythm: Part 2 (the link is to Part 1, but that's an introduction and the link to Part 2 is at the bottom. The Folk and Country basic strum pattern is the first one there).
You can use this pattern for
When the Sun Goes Down. Practic this pattern separately from switching chords, then bring the two together. You'll see how easily the two different mechanics can come together!