Sorry Boris, gotta disagree with you here.
Two options depending on the size of the site:
a) Small Site - use W2K box for AD, DNS, DHCP, setup a forwarder in DNS to your ISPs' DNS server(s), insert a host (A record) for those services on the SME box that you need to provide to the local network; under the Workgroup option tell SME to use the W2K box for WINS.
Setup email accounts on the SME seperately from W2K and maintain them seperately.
b) Larger site - as above to start but upgrade to Samba V3.x and use smbclient to sync users & passwords between both boxes. Don't enable SME as a domain controller when you have a W2K box or newer running AD as there are still some issues with Samba 3 & the replication; have a good read at
http://www.samba.org before any attempt at this.
I have been talking with James Price about updating his Samba V3 RPMS from the current V3 beta build to a recent stable version. He will be doing this as time permits but don't hold ya breath.
HTH