spec_r

Hi all, anyone can share some advice on servers? Currently using NT V4 but there are some limitations where NT can't communicate/access with Windows small business server 2003. So intend to upgrade OS but don't know which is a better choices.
I've look through microsoft web there are currently:
Windows Server 2003
Windows Small Business 2003 R2
Windows Server 2008
Windows Small Business Server 2008