Raising the Domain Functional Level … with a side of WTF?!

All,

As seen in previous questions, I have just taken over administration of this facility. In the wake of re-imaging @ 30 PCs riddled with viruses, I began to look at the domain setup.

From what I can tell the site was upgraded straight from NT4.0. This put the domain/forest functional level at Windows 2003
Interim.

We have 2 DCs for fault protection, of course … My question is 2.5-ish parts:

1) Do I just raise the functional level of the DC that is holding the FSMO roles and then wait for replication? … or do I have to execute the same procedure to both DCs?

2) What should I be on the look out for following the action?

Any advice/information … etc is appriciated.

Thank you,

Benjamin Egas