Small Business Server (SBS) is a line of server operating systems targeted at small businesses by bundling the operating system with a number of other Microsoft products that would normally need to be purchased or licensed separately. The most notable inclusions are Exchange, SQL Server, SharePoint and ISA/TMG (Microsoft's firewall and proxy server).
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Please check out our SBS 2003 to 2011 Standard Migration Guide: http://bit.ly/oZ5ePG
I believe you will find it very helpful. :)
Philip