Although these articles are not from a lawers perpective, it describes the process pretty well for the rest of us:
Coming into the USA under the TN visa.
http://www.naftaexchange.com/news.php?item.2.5
Getting H1 visa
http://www.naftaexchange.com/news.php?item.3.5
Coming into the USA under the TN visa.
http://www.naftaexchange.com/news.php?item.2.5
Getting H1 visa
http://www.naftaexchange.com/news.php?item.3.5