Before you take the plunge and try to set up a domain, lets talk about ePo.
We use ePo at my place, where we have an NT domain with some win2k member servers (the ePo machine being one of them). However we have some machines (mainly laptops) in a workgroup, and ePo handles them just as easily as the machines in the domain.
If the server itself needs to be on a domain, I would suggest setting up a box as an NT PDC. It will be much less of a headache for you, since a win2k AD will be overkill just to push out virus updates.