Fortunately for XP enthusiasts and Vista vetoers, the PC marketplace still has a loophole or two in it. In response to pressure from customers, Microsoft has made some concessions for people who really want XP, offering a lifeline for users willing and able to wade through the company's convoluted downgrading program. The upshot is that virtually every copy of Vista Business or Vista Ultimate Edition is sold with a license for XP, which a computer manufacturer can exercise to install XP Professional on any Vista Business or Vista Ultimate PC.
Inline with much of the discussion around here, I found this article pretty interesting. Seems to me like not very many companies know how to handle downgrades. I'm wondering if these downgrades are made difficult on purpose.