For partners that purchase and install SBS2003 R2 before October 31, 2008, there is a rebate up to $200 (in the US - please check your country in the drop down list on the rebate site). If you purchase Software Assurance there will be a free upgrade to SBS 2008. www.sbsrebate.com
To sign up for a preview of SBS2008 and get beta software, send email to preview@microsoft.com