I am missing something from the whole picture here. I know that in Microsoft Windows Server 2008, I am able to set up an active directory and then create my own domain name for my users. However, I don't know how to apply the domain name that I have and incorporate that with an actual email address. I.e. how do you sign up your domain name over the web for email? I am pretty much guessing at this point and my view on this seems pretty muddy to me. Any thoughts would be much appreciated. Thanks!!
Provided you have a domain name already registered with a registrar, it's simply a case of adding MX records on your DNS server which point to your email server of choice.
I might suggest though that if you have to ask this question and are seriously thinking about implementing email, that you either get some serious training on your email server of choice or go for some hosted service.