Some of the errors are my old-school fault, I guess...a few align=absmiddle and the like...but some are being caused either by DNN or my skin, I guess.  How do I know where these lines that fail validation reside?  For example:

< head id="Head" >< meta id="MetaDescription" name="DESCRIPTION" content... >

I think I can remove the first "id" in the head, but not sure on the second...and assuming this is a function of DNN when using the description box for the page?

I am getting some close slashes within the > like ...com" /> Would I just remove the "/" and close it the proper way like, say, < / a >? I am not sure how all this crap got in here, but blaming my skin until I hear further.

...and a lot of "leftmargin="0" topmargin="0" rightmargin="0" that I guess are no-gos.

Does this hurt SEO? I can live with all these errors, but not sure Mr. G can, so perhaps I need to appease Mr. G?  :)

Rather than posting 77 errors, I'll try to do the best I can figuring these out, but are there any sites/documents that might explain these errors and where one would find the culprit?

I thought two HEADS were better than one?

I looked at John's source...so < head id=.. > can be replaced with simply < head> and the < meta ID=... > can be changed to < meta name= > ? Like that? I learned HTML way before all this fancy dancy CSS nonsense, so I am at a total loss nowadays. :)

As for the margins, do they have to specified? If they are being set to zero, couldn't I just omit them? I'll do some research tonight, do some backups, and roll up my sleeves tomorrow, I guess.

These errors are not SEO friendly, I take it? If it doesn't matter, I can live with them rather than run the risk of screwing something up. :)

Although some sites cannot get away from it, malformed HTML is not SEO friendly.  However, unless it some how prevents the spider/bot from indexing your page, your content will still be indexed.  It is just that the algorithms will not rank you as well as you'd like. 

You only need to specify margins if it suits your design/layout.  And it would always be best to specify visual elements like that in the CSS file.