The instructions for importing Textpattern into WordPress work fine, however I think there are more things that can be done.
If you install WP into a different directory, and keep the Textpattern around as I have, then users who refer to your old RSS feeds will continue to get stale info. Instead you want your legacy Textpattern installtion to redirect to WordPress.
You can add a few lines to the top level index.php in the textpattern installation directory. Below, the yellow section is new, and the bold lines have to change to refer to your WP site: