Windows XP may be out of the retail market, but it still remains Microsoft's most cherished Operating System ever released even with top tier manufacturers like Dell or HP.
While consumers are resolutely setting their sights on the many flavours of Windows Vista; Business buyers are still thinking in Windows XP terms.
It is therefore not surprising that Dell managed to find a loophole in Microsoft's ironclad licensing conditions to preinstall Windows XP Professional with a Windows Vista License; whether Microsoft will tally these installations as Windows Vista PCs remains to be seen.
This also allows customers to change to Vista as and when they feel ready; obviously, this doesn't mean that you can use BOTH operating systems at the same time on the machine.
Dell is not alone in tricking Microsoft; other top tier PC manufacturers like HP are also bundling their computers with Windows XP Pro with a Vista Business Upgrade option as a "recovery media" as HP puts it.
The fact that Microsoft has not publicly lambasted Dell on the licensing issue indicates that the world's largest software company has gone soft.