Andy, if Vista is on your machine, live with it for a while and see how you get on. Although it has a few flaws, it also has some nice and useful features. It is also an advance for your colour work for the future because it has implemented WCS, at least, partially.
If you go back to XP, you'll likely need to have drivers at hand for your mother board chips, sound & graphics, network card, usb drivers, touchpad drivers, modem drivers, direct-X, upates for IE etc. You also will have to get virus protection and you'll loose any bundled software which may come with the new machine.
I lashed out on Vista to update my computer and I agree with Cod to some extent and I've gone back to Win 2K, mostly, (I use dual OS) but I've also been working with a new laptop and Vista using dual core processor and the more up to date interfaces and it works well and is pretty stable. It also contains lots of drivers for most things and what it doesn't have it will automatically find for you. However, if you have favourite older software, you may find that Vista will reject it. I knows about stuff which is incompatible and/or which Microsoft don't want you to use. It does have good compatibility modes for marginal stuff and it will look for fixes if necessary. You can revert the user interface back to Classic it you don't get on with the new, clumpy front end.