Now we shall know How-To access it...
1. Right click on the drive (e.g your DVD drive) where you have inserted your Windows XP CD & click 'open' or 'explore'
2. Open the folder named 'I386'
3. Search for a file named 'UNATTEND.TXT' which opens with notepad. Scroll down where you get to see the product key at the end of the file.