i want to migrate our website to Xhtml 5 or css 3.0 how to i migrate our site
Using HTML5 is one thing (most browsers won't support much of HTML5's APIs) get a book or find a site that outlines HTML5 and what it has to offer.
But if you want your site to validate as HTML5/CSS3, run your pages through W3C's HTML validator
use validate by URL > more options and choose your document type, in your case HTML 5.
Fix errors, repeat.
Keep in mind that there is no XHTML 5, only HTML 5. That's probably what you want.
While there are 3 different doctypes in HTML 4.01, there is only one in HTML 5:
<!DOCTYPE HTML>
Use that as your doctype when you migrate.
For CSS use W3C's CSS validator. Be sure to choose CSS3 in the options
Fix errors, repeat
do you really need to do that right now? keep in mind that broswers like Internet expplorer 6, 7 and Opera don't support CSS3 at the moment and even moere, if you care about valid CSS code, the current validator will not approve your code.
However, if you still want to do that, be aware to keep the most important parts of your code still compatible with mentioned broswers, and user CSS3 features (they are just awesome!) wisely. You could start learning here:
http://www.smashingmagazine.com/2009/06/15/take-your-design-to-the-next-level-with-css3/
There is also a good tutorial on nettuts, be sure to check it out (sorry, I cannot post more than one link here)
Once you have done, you could use CSS3, or CSS2.1 style sheets for different browser using conditional statements. Do some google research on it.
Hope this helps
i want to migrate our website to Xhtml 5 or css 3.0
For what reason?
HTML 5 has not yet reached Recommendation status and is still subject to change. Most of the significant changes in the spec aren't widely supported yet by browsers, either.
Same thing for CSS 3 - it has not been finalized, nor are many of its new attributes supported by all major browsers. You can start using CSS 3 stuff in your existing stylesheets, but be prepared for them to not work for many users yet.