Looks like this is the version I'll be buying. Was going to get an Upgrade
version but someone here posted that it won't allow an install of the 64-bit
version from within 32-bit XP (I don't have a 64-bit XP disc). I need it to
be future-proof so a full version it is, as I'm sure I'll be getting 64-bit
hardware in a year or two.

£219.99 seems to be the official price (Amazon UK and PC World online).
Similar price in Germany (Amazon.de)