As far as SBS 2003 or 2008, the only practical way you would be able to use it would be with a server in your own office. I am not sure how big your partnership is, but if it is a large business with many servers and their own IT people, they aren't going to run 20 servers with Linus or Windows Server 2008.
The only way I can see your using SBS would be if you had your own server. That's simply the only way.
Now, why use Small Business Server. Microsoft designed SBS 2003 specifically for small businesses. The main reason to use it is it gives you more functionality and is MUCH cheaper. If you bought Windows Server 2008, then you still pay for all the licenses. You then have to pay for Exchange Server 2010 at $1100 for five users. Each set of 5 CALs after that will run you nearly $400. Then you need SQL Server 2008. That will cost you dearly. Then the CALs for that. Of course, you could get SQL Express Edition for free, but now you have this hefty OS and SQL Express (which works fine for AC).
Now, here is what you get with SBS 2008. You get the core OS. It comes with Exchange Server without extra licenses. You get SQL Server 2005. AND, you GET Sharepoint. All this for about $650 for five users or per device. The extra CALs in five packs will run an edition $300 to $400. So, the cost difference is immense, and you get a lot more bang for your buck.
