Why do you NEED a full copy of Windows?
It still amazes me that people go on about the cost of Windows.
OK - Lets keep things nice and simple.
You've got WinXP Pro & WinXP Home
You've got OEM & Retail Upgrade
One of these 4 versions whould be what you are looking for in 99% of cases.
The difference?
Ultimately nothing in terms of the actual program, however with the Retail Upgrade the license is a lot more flexible.
You can move it from one machine to another for a start and it's not tied into any one piece of hardware.
WinXP Home OEM - £69inc
WinXP Home Retail Upgrade - £91inc
WinXP Pro OEM - £111inc
WinXP Pro Retail Upgrade - £175inc
Do you save money at the start but then have a restrictive license or pay that little bit more and have a license you can do a lot more with?
This is the same way most companies work, the more open your license the more you pay.
I've left off the Retail Full versions because most people simply don't need them.
Upgrade licenses are sold as a reward, call it a loyalty reward.
Instead of £250 for Windows you can have it for £175 because you're a previous user.
The majority of people only need WinXP Home - In a perfect world where piracy doesn't exist and Windows couldn't be thieved, ask those Pro users just how many of them would pay the extra for Pro because they needed the extra features - very small percentage.
Windows as a product hasn't really gone up in price in real terms since Windows 95 - the OEM and Retail prices are very similar.
One reason why it's difficult to describe Windows as a monopoly as anything which holds a monopoly tends to keep on increasing in price as people have no choice but to buy it.
Everyone has a Windows product to upgrade from, so use the "loyalty" discount and get the upgrade.
Don't moan at the price - decide which license is for you and spend accordingly.
Also look at the features of each OS and decide if you actually need the "top end" product, most people only need WinXP Home.
Also, finally.
Lets assume you need WinXP Pro and that you also decide you want the more useful retail license.
Now assume you're going to use that OS for what, 3 years minimum?
Even the £175 WinXP Pro Retail Upgrade has only cost you 16p a day - is it really that expensive?