Cheapest way to upgrade to Vista & Office 2007

Can I buy Vista & Office upgrades in the US to upgrade my XP Professional Desktop (in the UK).
looking at Amazon
Vista Premium is UK ?144.99 or US $153.99
Office Standard is UK ?153.99 or US $214.99
(need Outlook)
That totals UK ?324.98 or US $368.98 (=?194)

A worthwhile saving but will the upgrades register cross border as existing software UK sourced.