The page <URL:http://www.math.utah.edu/~beebe/html-check-notes.html>
describes exactly this procedure, and should tell you everything you
need to know. It talks about sgmls instead of nsgmls, but the two
should be interchangeable for this purpose.
>Am I totally off base here, or do I need to do something else,
>ie. reference the DTD in my HTML files, or ???
Yes, you'll need a <!DOCTYPE ...> declaration at the top of your
document to specify the DTD. The above page describes this.