I'm currently taking a course about coding in XHTML. Over the next few weeks I'll be gathering reference/resource links from that course and adding them to my resource page, linked in the title above. If you too are in the process of transitioning to XHTML from HTML (or wish you know how.....or wish you knew why :), you might want to check back once a week and see what's new in that section of the above page.
TIP: I highly recommend LVS Online. Really inexpensive, short courses that are very, very informative, fun, helpful. A great range of topics too!