The version available for download:
http://www.microsoft.com/downloads/en/details.aspx?familyid=635BE792-D8AD-49E3-ADA4-E2422C0AB424&displaylang=en
is as listed on that page:
"Supported Operating Systems: Windows 2000 Server;Windows Server 2003;Windows Vista;Windows XP"
We're running exchange 2007 on Windows Server 2008. (as some people who've listed having issues...?)
Is there a 2008 version that I've missed?