Microsoft announced on September 27, 2006 that SQL Server 2005 would be supported on Vista This is just more FUD from Stallman & Co. However you must have service Pack 2 installed for it to run. From the site:
"In an effort to provide customers with more secure products, Microsoft Windows Server "Longhorn" and Microsoft Windows Vista will only support SQL Server 2005 Service Pack 2 (SP2) or later when it becomes available. Earlier versions of SQL Server, including SQL Server 2000 (all editions including Desktop Engine edition, a.k.a MSDE), SQL Server 7.0, and SQL Server 6.5, will not be supported on Windows Server "Longhorn" or Windows Vista. Customers running applications with these earlier versions of SQL Server should consider evaluating and upgrading to SQL Server 2005, which was designed to take advantage of the upcoming security and performance enhancements in the operating environment."
You can read the whole story here
You can test SQL Server 2005 Service Pack 2 - Community Technology Preview (CTP) December 2006 right now