I worked out I was not making proper use of the values AdjustWindowRect() was setting. So now my sprites can move horizontally across the screen in bordered mode and look fine, but there's a problem: Everything looks squashed and sprites moving vertically still have the issue, because it's adjusting the top by -30 pixels and the left by -8 (because of the title bar). Ideally I'd like to have the window sized so that stuff within it is not squashed, unfortunately if I do it:
windowRect.right - windowRect.left,
windowRect.bottom - windowRect.left,
It looks fine and sprites move perfectly when moving horizontally, but the issue still exists when they move up or down.
I think this may be about solved now though, I just want to try and get the window sized correctly so sprites are not stretched and at the same time have their movement appear glitch free.