Hi Mikey,
Yup, tb is right on the button.
The dvd you have contains the files capable of installing all Editions. However, at the moment it has that little ei.cfg file in the sources folder.
That restricts it to installing Whatever Edition key you bought with it.
If you bought Pro Edition and got the dvd with that. You can use your dvd and your wife's Pro key to install on her machine.
If you bought a different Edition ( e.g. Home Premium) . then unless you delete that ei.cfg file - it will only be able to install Home Premium - and only in response to a Home Premium key.
You can of course, put the dvd in the drive on your wife's machine, rt click and copy the dvd - paste to another partition.
Then look in the sources folder - delete ei.cfg.
Then run setup from there and it will accept whatever Edition key you enter.
Or, once you have the dvd contents to a HD and dleted ei.cfg - just rebuild that into a bootable .iso and burn to dvd.
You can use that new dvd to install any Edition you put the key in for.
Very easy to do - and free:
Bootable ISO - Create from Installation Files - Windows 7 Forums