Generally speaking, none whatsoever.
Pretty much the only thing that you would have to do - and this does not
apply as you are adding a member server and not a WIN2003 Domain
Controller - is extend the Schema by running adprep /forestprep ( on the DC
that holds the FSMO Role of Schema Master ) and adprep /domainprep ( on the
DC that holds the FSMO Role of PDC Emulator in *E*A*C*H Domain ). I might
go ahead and do this anyway so that you can take advantage of some of the
improvements.....
However, if you are running Exchange 2000 then please be aware of the
'mangled attributes' issue that is well documented ( including a pretty easy
fix ).
However, as with everything in this industry - test in a lab environment
first!
HTH,
Cary