Need to purchase a copy of Windows XP

So, what you are saying is that even if it has been used (there are used £69 version which have been uninstalled), but as long as the original owner uninstalled it, it can be genuinely used again without breaching copyright?

Who knows if the original owner has not copied it and installs it again at some later date?

I would be careful buying from Ebay as i have bought software which appeard to be genuine when in fact it wasnt. Waste of money as it unusable due to copyright infringement. To be sure check the feedback from users as this will give a good indicaton as to whether what you have bought will work. I always buy from well established retailers. This may seem to cost more intially, but in the long term give you peace of mind.

This will explain the difference

6.      What is the difference between OEM product and Full-Packaged Product (FPP)?
ANSWER.  OEM products are intended to be preinstalled on hardware before the end user purchases the product.  They are “shrink wrapped” and do not come in a box like the retail products do.  Full-Packaged Product (FPP) is boxed with CD(s), manuals, and the EULA and is sold in retail stores in individual boxes.  The End User License Agreements (commonly referred to as “EULAs”) for OEM and FPP products are slightly different.  One main difference is that an OEM operating system license (such as the license for Windows) cannot be transferred from its original PC to another PC.   However, the FPP version of Windows may be transferred to another PC as long as the EULA, manual and media (such as the backup CD) accompany the transfer to the

That's the risk you take with the online auction sites
The EULA for Windows XP Pro allows a one time transfer of the retail package (Section 4 - Transfer to Third Party) by the original purchaser but the whole packege needs to be included including the original certificate and media. (And you need to be sure your not getting a cheaper System Builder/OEM or other version instead).

Was the original system provided with XP?

No, the original system was a self built one.  Assume no operating system on there.

So, in summary, if I have read the above comments correctly, I take it that YES, i can purchase a USED copy of Win Xp as long as the whole package is provided and that the userkey and software has been uninstalled by the original user?

Yes thats correct

Depending on when the system was last installed you may get flagged for telephone activation though, that's when you need to be sure you have a retail version.

I presume that I am protected by Amazon, even if bought on Market Place because ultimately Amazon is still promoting the seller through that medium, if it turns out to be either pirate copy of non legit?

My experience with Marketplace is it's no safer than eBay - Amazon will arbitrate in the same way eBay does but ultimately your gripe would be with the seller.

http://www.ebay.co.uk/itm/Microsoft-Windows-XP-Pro-SP3-Professional-OEM-Edition-COA-Product-Key-/170754561740?pt=UK_Computing_Software_Software_SR&hash=item27c1c3d6cc

What do you think of the above?  I think they're getting around this because they know that nobody will want to collect the old PC.  

will it work? his company seems to be going for several years without an issue?
What about the MAR version which he is also selling?