[exim] HowTo for DomainKeys

Hi, list!

I'd like to implement DomainKeys for my server...

Has someone already done it? Can I have an example of Exim-Configure to check
for incoming E-Mails and an example to add the Header by outgoing E-Mails?
Or the URL of a good HowTo...

Then, the great question (I didn't understood it): have I to register my key
(as like as an HTTPS-Certificate) or not?
If yes, how does it cost?

Another question: I use Exim 4.66. Is it enough? Or must I upgrade to 4.67?

Thanks a lot for your help!
Luca Bertoncello
(lucabert@???)