whilst all the configs for all the versions of win 7 are on all win 7 disks, you may have an additional file which prevents the wrong version being installed. you will know what versions can be installed from what disk, if you get an option of which version ie, home premium, professional, etc. they are the ones that will install any version. if the disk allows only home premium, then all versions are still there, but their is an addition file in the sources folder, ei.cfg you could copy the entire cd to a bootable external hd, remove the ei.cfg file from the sources directory, and you would then be able to install any version (license permitting).
Sorry chap, obviously I didn't read the first line of your post where you said you had the licence key. My bad, apologies for that.
As it is well known it is indeed this ei.cfg file that 'tells' the PC what distribution route it was intended for, mine for example looks like this; [EditionID] Professional <= OR Home Premium, Ultimate etc... [Channel] Retail <= OR OEM [VL] 0 as I bought it from Scan. If you have issues installing using the disc your friend has, then rip the disk ~2.32GB, unpack it (I use WinRAR) and just delete the file ei.cfg which is under the folder 'sources'. Then recompile it into a .iso (I use this guide but with Imgburn instead http://bit.ly/eeVKVX it works fine, the options aren't on identical menus, but its pretty much identical if you look), burn it to DVD and then you wont have any issues. Incidentally you also have the benefit of that disc becoming 'magic' as it will allow you to install any version of the software (but only x86 if its an x86 disc or x64 if its an x64 disc). Hope that helps
Worked great thanks!!! Got rid of the ei.cfg file & was prompted for the version just after setup. Thanks for all the help guys.
