It seems there is a new philosophy on Windows operating systems. A business manager from Tarsus Technologies is recommending that you buy computers with Windows Vista, but keep using Windows XP. This may be a bit confusing, but it makes sense.
The important thing to consider is that Microsoft is continually making Vista better everyday till the point where it is much better to use Vista than XP. This means that if you have a Vista license already, then you don't need to buy it later. You already have a XP license sitting around somewhere so you could just use that in the meanwhile. This is quite an interesting strategy.