Windows 2003 server Vs. SBS 2003

we have a workforce of 25 users and at no period we are going to cross 50 users and we are planning to get new server ,now I would like to know if i go for SBS 2003 what are the major advantages and disadvantages w.r.t Windows 2003 server...such as features,CAL,Devices,Microsoft Hidden Strategy,
Loss in terms of future additions of clients. Performance between s/w applications in sbs2003 and software?s if we buy separately for Win2003 server.etc
Thanks in advance