Aria have put together a special page for HotUKDeals members with the best prices for the new Windows Vista. They have told us these are the cheapest prices on the market, and from our checks that seems to be true but if you see otherwise let us know!!
Prices start from £52.29 inc. VAT for Vista Home Basic OEM. Shipping is £4.69 by Royal Mail. The prices will be available until January 26th.
Alternatively, you can buy Microsoft Windows XP Media Center, because it includes a Vista Express Upgrade Coupon (which gets you Vista Home Premium for £8 (just to cover the P&P supposedly)) from eBuyer for £74.41 - two operating systems for the price of one!). LINK: http://www.ebuyer.com/UK/product/119649
Sorry, first edit I've made!