You need to specify at the time of purchase that you would like it to be upgraded from Vista to XP.
With Dell, on their desktops, it is £60 to go from Vista Home to XP Pro (no cost for XP Home, but Pro is just that little bit more.
With a laptop, it can be a bit of a pain to "retro-fit" XP on it due to specialist drivers required.
That said its not impossible, you could MAYBE get away with taking it back and playing dumb and say "this software doesnt work, make it work, oh you cant, then my money back please - it works fine in XP, and when I ordered it I was not warned that the software I need to run on it would not".
For the last bit you could always slip Hovis £5 and have him go in and say "Dun wurk, fixit"
