I get this question all of the time on the discussion forum and this blog, so I feel I should help to spread the news.
SAS now supports SAS 9.1.3 SP4 on Windows 2008 (32-bit edition). Here is the official statement.
Update 07Oct2009: I changed this to indicate that the official support policy is that the 32-bit version of Windows Server 2008 is supported, and not the 64-bit version of the OS. However, SAS 9.2 Maintenance 2 does support both 32- and 64-bit Windows 2008.
Support for SAS 9.2 will be delivered with the SAS 9.2 Maintenance 2 release, which is imminent*.
* "imminent" is a word which here means: Real Soon Now, or Just Weeks Away. Less than a month. Before my next birthday.