Exchange 5.5 and Win 2k/2k3

I have a WinNT domain with a PDC and BDC and will upgrade to them to Win 2003 DC’s. I have an Exchange 5.5 server running on a Win 2k member server. We will upgrade Exchange in the future but not immediately.
Will Exchange 5.5 work with Win 2k3?
What kind of problems am I going to need to look out for when I upgrade the Domain Controllers as far as Exchange is concerned?
What mode will 2k3 Active directory need to be run in?
Good links would be helpful.