I know the games workshop website has FAQs about the codexes, I believe to make them compliant with the 4th edition rules. Also, if the rumors are true, I think we'll be having a new Tau Codex in a few months.
Check the GW site for the updates, or wait to see what comes.
BTW- Check out the sneak-peeks at GW of all the new Tau units in their "Greater Goodness"
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