I have a Windows 7 Ultimate DVD, and I need to Install a Windows 7 Home premium (I got this license from windowslifestyle.com, thanks Nitin. It was on July 15th 2010). Today I wanted to use the key, but could not find a good installation disk.
After a search I found that all Windows 7 Installation DVDs contains all Windows 7 Editions, and what you need is to delete a file ei.cfg" inside the source folder. So I did the following
1. Created and ISO image of my Windows 7 Ultimate DVD
2. Used ei.cfg Removal Utility, which will remove the ei.cfg from the ISO - You can get ei.cfg Removal Utility from here
The ei.cfg Removal Utility is a simple tool that will remove the ei.cfg from any Windows 7 ISO disc image, thereby converting the image into a "universal disc" that will prompt the user to select an edition during setup.
3. Burned the ISO to a DVD and used that for installation (You can mark this DVD as an Any edition Windows 7 DVD 
)
After the option to select install a screen with all the windows 7 Editions will come up, you can see the screen below
This will be really helpful if you have one windows 7 edition DVD and need to Install another edition of windows 7.