About two weeks ago, Windows Vista and the 2007 Microsoft Office System were finished and are being prepared for "release to manufacturing" as we speak.
If you have an MSDN software subscription, you can find Vista RTM (x86) and some parts of Office 2007 RTM right now! (Though I haven't seen the Office 2007 RTM servers yet...) Most everyone else will have to wait until January to buy the boxed versions of Vista and Office 2007 or get them on new PCs.
If you happen to buy a new PC between now and then, you'll probably be able to upgrade to Vista for free or low cost via the Windows Vista Express Upgrade program. Most major PC manufacturers are listed, so if you're itching for that new PC or laptop (as we are) you can rest assured that you will get your Vista upgrade for free or almost free. If you want to stick to Windows XP (e.g. if you are afraid of Vista), buy now before the end of January so you can guarantee Windows XP is on your machine!