PC World have thrown up their Pre-Order page for Windows Vista! (see PC World source)
Vista Home Basic is Â£154.99 inc VAT
Vista Home Premium is Â£184.99 inc VAT
Vista Business is Â£250.00 inc VAT
Vista Ultimate Â£325.00 inc VAT
Here is a small price comparison from windows XP please note the prices i post are from ebuyer.
Windows XP Home: Â£140.95 Inc. VAT
Windows XP Pro: Â£220.00 Inc. VAT
From this simple comparison its easy to see the biggest difference in price is that of Vista Home Premium Being alot cheaper than XP Pro.
Currently there arent any prices for OEM copies, but from general knowledge they will most likely be alot cheaper than the retail packaged versions.