When I focus my Canon 350d I connect to the laptop, open up a capture program (I use ImagesPlus), open the Focus Tool window and I set the image time to 2.5 seconds.
Then I let the camera repeatedly snap away, and I focus the images as they come in every 2.5 seconds.
The ImagesPlus Focus tool has a graph showing when you are at best focus.
If you don't have ImagesPlus, or a Focusing tool, just take an image repeating automatically every 2.5 seconds to get a nice image to focus on.
I think most capture programs allow you to download an image automatically repeating.
