As at 14/11/2008
Review the system requirements to determine the minimum and recommended system requirements needed to run Windows Small Business Server 2008 Standard and Windows Small Business Server 2008 Premium Release Candidate 0 (RC0). Windows Small Business Server 2008 supports a maximum of 75 users or devices.
Small Business Server (applies to Standard and Premium)

Component	Requirement
Processor	Recommended: 2 GHz (x64 processor) or faster
Memory:	Minimum: 4 GB RAM Maximum: 32 GB
Available Disk Space:	Minimum: 60 GB
Fax Modem:	Fax Services require fax modem

Additional Server (applies to Premium only)

Component	Requirement
Processor	Recommended: 2 GHz (x86 and x64 processors) or faster
Memory:	Recommended: 2 GB RAM Maximum 32 GB (x64) or 4GB
Available Disk Space:	Minimum: 10 GB Recommended: 40 GB
Fax Modem:	Fax Services require fax modem

Both Servers

Component	Requirement
Network Card:	Ethernet network interface card from the Windows Server Catalog
Internet:	Some Internet functionality may require Internet access (fees may apply) and a Windows Live ID Account.
Supported Client Operating Systems:	Microsoft Windows XP Professional Edition SP2 or later; Windows Vista Business, Enterprise, and Ultimate; Windows Mobile 5.0 or later
Fax Modem:	Fax Services require fax modem

Additional requirements:

* DVD-ROM drive
* Super-VGA (800 × 600) or higher-resolution monitor
* Keyboard and Microsoft Mouse or compatible pointing device
* Internet access (fees may apply)

Actual requirements will vary based on your system configuration and the applications and features you choose to install. Processor performance is dependent upon not only the clock frequency of the processor, but also on the number of cores and the size of the processor cache. Disk space requirements for the system partition are approximate. Additional available hard-disk space may be required if you are installing over a network.
For those planning to migrate from Windows Small Business Server 2003 R2 to Windows Small Business Server 2008

A smooth migration to new software/hardware is what’s most important for small businesses. Our research shows small businesses purchase new hardware with software infrastructure upgrades. Therefore, we have focused on providing guidance, wizards, and automation for fast, easy migration to Windows Small Business Server 2008 on new hardware. For the migration scenario from Windows Small Business Server 2003 R2 to Windows Small Business Server 2008, a manual migration will be required. More information will be provided in the future.
Notes:

*For a list of specific supported hardware, see the Windows Server Catalog. By design, for supported hardware, Windows Small Business Server 2008 uses the Windows Server Catalog.
*All server hardware should meet the requirements established for the Windows Server 2008 Logo Program for Systems. You can learn more about these requirements by visiting http://www.microsoft.com/whdc/winlogo/hwrequirements.mspx.