It Is possible to code HTML for a kind of 'infinite backwards
compatibility', that is, each new function that an old browser
doesn't support just vanishes, but the text remains... So, if
you are clever and have too much time on your hands, you
can make a "modern" site that retains this text content while
the bells and whistles fall off. This isn't a <noframes> thing
since that actually makes you code the page twice. It's more
like making an image that looks as good in B&W as it does
in color, with the same pixels.
All being said, code the fancy one, make a sed script that
strips it down to a basic level so you need only spend 10
minutes cleaning that one up for final approval, then make the
basic one default and put a link on that page to the fancy one,
for the modern visitors.
If any of this is too much work: do the basic.
John A.