I just received an e-mail from Microsoft Connect regarding the release of Windows Server 2003 SP2 RC (build 2825). I'm not sure if Microsoft will make this available outside Connect (like they've been doing with the SQL Server 2005 SP2 CTPs). However, if you have a Connect account, check out the 'Available Connections' page and see if you can join in. According to the Windows Service Pack Roadmap, SP2 is scheduled for release in Q1 2007.
Update 1: Microsoft just posted the SP2 RC release notes for public consumption.
Update 2: Looks like they've decided to release the SP2 RC software as well.