Vista, and it's companion programs, Office 2007 ...- its.
A rule to remember - If it can be replaced by "it is" then use "it's". If it's possessive, use "its". Similarly with "who's" and "whose", etc.
I don't know if you want to mention a couple of other things:
1) Vista was apparently released early to satisfy the contracts with customers who bought Software Assurance (often under duress).
2) I believe the Business and/or Enterprise versions of Vista don't include DVD burning software. (I think I posted a link about that months ago, but I can't find it.) You'd need Home Premium or Ultimate but you can't get Ultimate on SA. So you have to buy burning software from another vendor. [link|http://www.microsoft.com/presspass/press/2006/feb06/02-26WinVistaProductsPR.mspx|MS's explanation of the various offerings].
Vista could be MS's newfangled DOS 4 or Waterloo.
Cheers,
Scott.