I contacted Jason Zimdars, author of the design, and he gave me 3
solutions. So, first, we should decide what to do: leave it as it is,
with validation errors, or fix it, possibly changing a bit the look of
the site (rounded corners and stuff).
And second, we'd need a volunteer for this, as I'm not good with CSS,
I don't feel able for this task.
You'll find below Jason's reply. What do you think we should do?
Oh c'mon. Validation is an tool, not a wonderful thing in its own right. Making the site look worse in good browsers, or requiring extra work from the designer (who isn't getting paid) just so we can check off the "valid CSS" box are both bad ideas.
My vote: leave it as is. We're grown up enough to stand the horror of not being valid.
I am sure your effort with XHTML will pay off, and I hope those
reported issues in IE8 are fixed now (can't test it myself).
CSS is a different story in my view. If validation was trivial to
accomplish I'd say go for it, but since it is not I'd touch that only
if the site looks horrible in some mainstream and modern browser.