A while back, Meredith asked about instructions for this block - unfortunately, her comments are set to no-reply, so I have no way to email her back, but perhaps if you're reading here, Meredith, you'll still be able to see this!
I don't really have a patter for this, per se, but it's easy to do. What you need for each block is 8 rectangles 2.5x4.5" of the background fabric and 4 squares 2.5x2.5" of the pinwheel fabric. Then you use the stitch across the diagonal method with half the rectangles and all of the squares - i.e. draw a diagonal line across the centres of the squares, place the square right side to at the top of one rectange and stitch across the diagonal - you can then trim and press so you have a rectangle with a triangle top - one "leg" of the windmill. Make sure you do all four with the same direction on the slant of the diagonal.
Then, just join one of these pieced rectangles to a plain rectangle and then join the resulting four square pieces into a windmill piece. It's all very straightforward and easy... Hope that makes sense!