I'd say it's a very blurry line (and as many similar cases: It's always better to ask a lawyer).
As for your first question, the HTML code (the code itself) would probably not violate the clause. The CSS and images, on the other side, might.
No Derivative Works — You may not alter, transform, or build upon this
work.
Looking at the definition of No Derivative, I can easily imagine this being applied to graphics (the author not wanting someone to grab an icon and change a nice pastel tone for a shinny red, for example). However, writing some HTML that imitates the layout sounds like too long of a stretch for me.
Now, this is my personal point of view, but the whole idea behind the copyleft and later the Creative Commons movements is that all knowledge is, in some aspect, actually derivative. Nobody creates something completely new, and nobody owns knowledge of something itself. You can choose from a set of more or less flexible licenses, this one being one of the most popular ones, and it's important that you always try to be faithful to them. But when the line gets blurry (like with HTML in this case), it honestly comes down to what you feel comfortable doing.
From the CC's FAQ:
Whether a modification is considered an adaptation for the purpose of
CC licenses depends on the applicable law. Generally, a modification
rises to the level of an adaptation when the modified work is based on
the prior work but manifests sufficient new creativity to be
copyrightable, such as a translation of a novel from one language to
another, or the creation of a screenplay based on a novel. Under CC
licenses, syncing music in timed-relation with a moving image is
always considered an adaptation.
I think it will depend on how much you want to reproduce from it, so to answer your second question, I'd say: In cases like this, it's not so much a matter of licenses, it's a matter of good faith / ethics. If you put enough effort and enough 'of you' to call the final result completely yours, you will be creating something considered completely new, and the derivative part will only be an inspiration.
