Yep, that COA is proof that you own a licensed copy of XP (having a physical installation CD means nothing).
 
When you come to install XP, make sure that you have an OEM version of the installation CD for the edition printed on the COA (Home or Pro). They use slightly different product keys, ie. retail vs oem and won't accept the 'other' key.
 
If you haven't got an OEM CD, you can usually find these cheap on eBay, but make sure that you get one that installs on any hardware as some are tailored to a particular vendor - Dell for instance - and apparently won't install on non-Dell gear. Also note that OEM installations still need activating.
 
I am pretty sure (until I am corrected ) that borrowing a friend's disc and installing from that (even taking a copy) still keeps you in the green. The COA is the important bit.
 

Originally posted by ross_aveling:

Quote: 
I am pretty sure (until I am corrected ) that borrowing a friend's disc and installing from that (even taking a copy) still keeps you in the green. The COA is the important bit.

 
You are correct its the licence serial code that is your proof of authenticity.
 
I use the same OEM XPhome and XPPro cds for repairs to customers pcs
 

The issue here is wether Microsoft will allow the seller to transfer said COA or not.
 
I bet if you really want to get to brass tacks on this one you will really be obliged to purchase a retail copy of XP Home/Pro instead of an OEM version

Actually, since an OEM license from Microsoft is 'tied' to the hardware, it is REQUIRED to accompany the hardware when/if the hardware is sold.

Originally posted by adamvjackson:

Quote:Actually, since an OEM license from Microsoft is 'tied' to the hardware, it is REQUIRED to accompany the hardware when/if the hardware is sold. 
So technically, the eBay seller didn't have the right to sell said notebook with the accompining OEM sticker huh ?!?

The pertinent parts of the microsoft EULA are:

Code:

"...1. GRANT OF LICENSE. Microsoft grants you the following rights provided that you comply with all terms and conditions of this EULA:1.1 Installation and use. You may install, use, access, display and run one copy of the Software on a single computer, such as a workstation, terminal or other device ("Workstation Computer" ). The Software may not be used by more than one processor at any one time on any single Workstation Computer....3. RESERVATION OF RIGHTS AND OWNERSHIP. Microsoft reserves all rights not expressly granted to you in this EULA. The Software is protected by copyright and other intellectual property laws and treaties. Microsoft or its suppliers own the title, copyright, and other intellectual property rights in the Software. The Software is licensed, not sold....13. SOFTWARE TRANSFER. Internal. You may move the Software to a different Workstation Computer. After the transfer, you must completely remove the Software from the former Workstation Computer. Transfer to Third Party. The initial user of the Software may make a one-time permanent transfer of this EULA and Software to another end user, provided the initial user retains no copies of the Software. This transfer must include all of the Software (including all component parts, the media and printed materials, any upgrades, this EULA, and, if applicable, the Certificate of Authenticity). The transfer may not be an indirect transfer, such as a consignment. Prior to the transfer, the end user receiving the Software must agree to all the EULA terms...."

According to the above, you're in the clear...but the eBay seller might have unfulfilled obligations with respect to the "component parts, the media and printed materials, any upgrades, this EULA" clause.
 
If you want a real laugh, read paragraphs 15 through 22 of their EULA.
You basically have NO warranty and NO remedy for damages caused by their software. Even if microsoft knowingly sells you software that won't work as advertised, or is possessed of any of a long list of specific or general flaws.