Thing is, I've got a desktop computer that I've thrown together from spare parts and have 2003 installed on it, just so I can't learn the basic functions of the OS. I've been doing this for about 8 months. Don't have money to buy a system for installing 2008 or 2012, yet. But while I'm saving my pennies, I'm trying to determine whether it's worth putting time into learning 2003.
I would think so since a lot of the basic functionality of Windows Server doesn't seem to have changed...ie Active Directory, organizational units, group policy, folder redirection, roaming profiles, trusts... When moving into later versions the learning curve won't be bad since I have a feel for the basics.
I figure another year of using 2003, I'll be able to afford a new system for installing 2008 or 2012, and I'll be ready to take on those businesses who don't want to upgrade from 2003 (and since 2003 and 2K are similar, I can probably handle 2k without much trouble, if necessary). Around February next year I plan to get a loan from my bank to help me get my business started because my credit will have significantly improved, and I'll buy my new Server (test) system at that time.