During the operating system portion of the Small Business Server 2011 Standard installation, you will reach a screen that asks what type of installation do you want. The options here are two: Upgrade or Custom (advanced). You can only use the Custom (advanced) option to successfully install SBS 2011 Standard, there is NO in-place upgrade path from previous versions of Windows or SBS.
SBS 2011 Standard is built on top of Windows Server 2008 R2 Standard and this is a behavior that derives from that integration.
If you want to add SBS 2011 Standard to a network where SBS already exists, you will need to follow the migration documentation found here.
This documentation will also help you add SBS 2011 Standard to an existing domain where there is no SBS product currently in place.
[tags]small business server 2011,sbs 2011[/tags]