It depends what you call a network. But you certainlyu don't need more than what ou have. SBS 2008 has a lot of new features over 2003. But, it looks like you are talking Windows Server 2003 and not the SBS version. The problem with 2003 is I don't believe you can run 64-bit on it, so you are limited on RAM.
There is a Windows Server 2003 R2 x64. SBS 2011 is pretty good too. It's about 760 with 5 User CALs.
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