I have successfully integrated WP within my design. The blog works. But when I go to validate it at w3, the validator has problems with the WP's doctype inside the design.
DocTypes are usually at the beginning of the page. That validates fine. But then where I have included the WP, it has a problem with its DocType that appears in the middle of the file. Unfortunately, I can't give you a link because it is considered Google Juicing. So I don't know how this can be solved if a person can't see the problem.