is there any way to install windows xp pro using the coa I have on the case of a computer I bought ? I was told this was possible . Do'nt you have to have the original cd with the matching coa or product code ?

What you are proposing is illegal and against the End UsersLicense Agreement that is attached to every installation of windows operating systems...basically it is one license per computer and it cannot be transfered without the computer it is attached to...
This is simple
1) you may transfer the computer and all installed software to another person...but you cannot retain any copies of the software
2) the operating system is attached to the computer if the computer dies...the operating system dies with it.

There is an exception to this....If you have a Retail or Corporate
License...then these are allowed to be installed on as many computers as the license allow for....Retail 3or 5.......corporate...normally from 25 +

There is no way to determine the installation disc matches the license...but it must be the same type for the license to install and activate...
Retail must use a Retail License
Corporate must use a Corporate (volume) License
Upgrade must use upgrade License
OEM must use OEM license......if you purchased a branded computer such as Dell or HP then in most cases this is what you have.

Branded Computers usually slipstream their products. This means that the operating system and drivers are combined on a single disc and is designed for that single model of computer. Installing this to another computer could be hazardous to that computer because of the improper installation of the wrong driver files.

Edit: If you are using the installation CD to install to the same computer that the COA is attached to then this is acceptable so long as the right disc for the right license....XP Home and XP Pro and XP Media center are all different products and will have their own specific installation CD's to match their respective License (COA). It is illegal to use that attached COA on a different computer

A user can install the Windows XP OS using the product key indicated in the COA (Certificate of Authenticity) on the body of the PC, if one has the pre-packaged installer CD necessary to complete the process. Using an installer CD from a different SKU (Stock-Keeping Unit) will not work with that COA, as the product keys are distinct and different for each one.

Validate the authenticity of the Windows OS by inspecting the COA affixed to your computer. A pre-installed OSs COA has the Microsoft brand printed on the label, plus a product key of 25 characters.

An OEM version differs from the retail variant. The COA from an OEM matches the PC it was made for. The COA sticker for this version has the name of the manufacturer. The copy was created for the pre-installed PC, and the same COAs product key will not work on another computer.

The retail Windows OSs usually come with the COA affixed to the box. This OS version can only be installed on one PC at a time. If the PC (wherein Windows was installed) breaks down, use the sticker and software from the same SKU to install it in another PC.

If you have the original installer CD, you can re-install Windows XP by simply running a clean install. This will work if your COA sticker and CD are genuine, and the COA matches your disc. If the COA is labeled XP Home, for example, then the installer CD must also indicate this. Checking on Microsoft’s website is another option to verify if your COA is legitimate.

Note that one may not be able to install Windows OS if you own a PC with a COA without having the CD. A COA with a matching original installer will ensure proper installation. In addition, drastic hardware change may affect Windows installation. It may occur that you will not be able to install the OEM copy as Windows may detect that you now have a different PC.

That's what I thought . what is the point then of sellers on ebay and other places putting in the description that the computer they are selling has a coa on the case ? It is useless is it not ?

sounds like you have alot of knowledge on this subject,thanks

Not at all. If you buy a computer with a COA on that case then it is an assurance that the operating system is legal to transfer from one individual to another...If there is no COA (for the operating system installed on the computer) involved with the sale then you should not buy it...as it is a strong possibility that it is pirated software.

There are a lot of ebay sellers quoting that the computer has an attached COA and thus making the pretense of a legal sale that when delivered the COA is not the same type as the operating system that is installed. That is pirated software and the sale is illegal....Tha COA attached must match the same type as the operating sytem that is installed for the sale to be legal.

Once it is determined that the COA is legit and matches the installed operating system then that coa can continue to be used for reinstallion of the operating system to the computer the COA is attached to....it cannot be transfered to another computer legally!

Had a BIG OEM (I forget who) built system with a trash install of MCE 2005 We had no media disc at all. Cust was on a budget. IE...... No money for Disc.

On a whim I grabed my Win XP pro disc OEM (Frys electronics) there COA numbers and installed pro. It work perfectly although it did ID it self as MCE it did not have the added programs that would be loaded from disc 2.

Customer was thrilled and happy.

Jim