I wondered exactly the same thing so I e-mailed Microsoft UK and thus is the response I got from them:
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Dear Mr. Bookless
Thank you for contacting the Microsoft® U.K. Beta Programme regarding Microsoft® Preview Programme® software.
I can confirm that we have recieved the Microsoft® Windows® XP Beta order that you placed . We are currently awaiting stock to arrive for this product and until such a time no payment will be taken from your credit card.
We currentlty anticipate that fulfillment of all pre-orders will be around mid July, although,as yet, we do not have a final confirmation on an exact date.
In order to evaluate Microsoft® Windows® XP within the UK, it will require you waiting for the Beta CD to be sent to you.
If you have any further questions, please feel free to contact us
Yours sincerely,
David Treanor
Beta Contact Executive
Microsoft Connection