Ironically Redmond isn't switching off the security updates on its more popular, but much older operating systems - Windows XP SP2, as well as all version of Windows 2000 until July. Microsoft's Eric Ligman warned on the company's SMB community blog th that engineers may not be able to help resolve this until you have upgraded to a supported level.
Vista is currently on Service Pack 2 and Microsoft considers this as a "bare minimum" for decent support.
