The SBS 2003 R2 Technology Upgrade Program (TUP) ordering website is now live and taking orders.  See http://www.microsoft.com/windowsserver2003/sbs/r2/upgrade.mspx for eligibility requirements.  From the page:

How do I qualify for this program?

To be eligible, customers must purchase Windows Small Business Server 2003 with SP1 (Standard or Premium Edition) preinstalled on a new server from an OEM or System Builder partner during the eligibility period. Purchases of SBS 2003 through a software retailer (full packaged product), an applications vendor, or a Volume Licensing agreement are not eligible.

The Program eligibility dates are as follows:

English Language versions

March 1, 2006 through August 31, 2006

Non-English Language versions

March 1, 2006 through September 30, 2006

 
On that page, you’ll find this link, which takes you to the ordering site:  https://upgradeweb.moduslink.com/