Retiring SBS2000 with new SBS2008 Server

I know there is no direct upgrade path and I don't have any intentions of going that way.  I basically want to join the sbs2008 box to the current SBS2000's domain.   Promote the SBS2008 and demote the SBS2000(and trash it).   I don't really want to copy XP profiles and such.  Is that possible to do without causing me more headaches than just starting a new domain ?  

what are my steps to keeping the same domain in place ?

Also is it easy to move between the 2 different exchange servers or should I just be exporting all the Exch 2000 mailboxes to PST's ??

thanks,
Paul