[XHTML 2] Browser Compliance Question

I'm trying to make sure that my sites will be backwards compliant for old
browsers if I use XHTML 2.. 

>From what I understand, I can use XSLT to produce a re-worked xhtml1
rendering of the pages I'm using.  Then I can use browser sniffing or
http-accept, to make sure that older browsers get my normal XHTML and  XHTML
2 complaint browsers are served the newer XHTML 2 version of my code. 

Would this work? Would it even be worth my time? 

Thanks,

David Lieberman

http://www.awdsf.com <http://www.awdsf.com/>