Fact 1: As of June 30, large computer manufacturers such as Dell and Hewlett-Packard can no longer offer Windows XP preinstalled on new computers, though Microsoft has said it would consider re-evaluating the deadline if there's enough customer demand.
Fact 2: Anyone who buys a copy of either the Business or Ultimate versions of Vista is entitled to also get Windows XP Professional .* Each computer manufacturer decides whether, or how, to implement this.
According to CNet, Dell will continue to install Windows XP for you on their PC even after the date given by Microsoft.
When selecting your operating system, you will see an option called "Genuine Windows® Vista Business BONUS" and "Genuine Windows Vista Ultimate BONUS." With these options, you may...have Dell factory install Windows XP Professional. You will also receive a backup media disc for Windows XP Professional, as well as the media for Windows Vista.
In other words, Dell provides optical discs for both XP and Vista, so you can change over at any time. This is not like
Apple's Boot Camp, however; the computer can have only one operating installed on the hard disk at a time. But Dell provides technical support for both XP and Vista. Whether its tech support is worthwhile is another matter.
I hope other company will follow their steps to continue supporting XP at least until it became "more stable and worthy" (well.. even XP got their own problem back then when Microsoft first release it).