questionabout valid HTML and valid CSS

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I've spent the better part of 3 days trying to get validation on the
attached file. The HTML validator says that the file is valid HTML
4.01 transitional, but when I link the file to either an HTML or an
XHTML file, I get a lot of errors with css-validator not recognizing
the HTML, where I thought it should leave it like that and not worry.

Can you provide some guidance as to where the problem is?

Thank you

PS: The document has the stylesheet in question incorporated as part
of the page, I've had even less success when trying to link to it
using HTML's link attribute

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