You can obtain the Winxp key from a corrupt XP install as long as you
can get to the windows directory. try the following.
1. ghost the hard drive to an image.
2. extract the windows directory from the image and put it somewhere
safe i.e. myDocs.
3. Download the latest version of Magical Jelly Bean Keyfinder from
http://www.magicaljellybean.com/
4. Open the Keyfinder and select "Tools>Load Hive".
5. Browse for the windows directory you extracted from the image and
click "ok"
The key will magically appear in the open window.
As I mentioned you must be able to access the Windows directory on the
target machine. If you can simply copy this directory straight off
the hard drive it will do...But if the hard drive is partially corrupt
from bad sectors, any type of access often will cause further damage.
Therefore I recommend imaging the drive first up, it will give you
more chance of data recovery too.
In terms of using OEM media this should work as long as the target pc
is not from HP, Dell or the likes.