One of the questions that I got this week at DevDays was on the supported Windows platform for DPAPI (Data Protection API). It turns out that it originally showed up for the Windows 2000 platform. So that platform and any later releases (XP, Windows Server 2003) will have this capability. If you don’t have access to the DevDays wrapper class for the DPAPI, see How To: Create a DPAPI Library.
Another good point is that DPAPI support will be built into the next framework as System.Security.Cryptography.ProtectedData. I really look forward to Visual Studio 2005.