SQL Server 2005 Service Pack 2 has been released today. It is needed in order to run MS SQL Server smoothly on Vista machine.
I run MS SQL 2005 Express/Standard on my Vista box but I had to turn off UAC (which is not recommended).
Beside this there are many improvements as you can see in What's New in SQL Server 2005 SP2
Download SQL Server 2005 Service Pack 2
Through Marto Kulov's blog.