Copy the dvd to disk:
dd if=/dev/sr0 of=win7.iso
There is a file called ei.cfg that defines which installation flavour you have. If its not present, windows will ask you which version you want. Besids from that, the install media are all the same. The trick is described in various blogs, e.g. this one.
In order to modify the iso (delete ei.cfg ), do the following:
mkdir mpoint
sudo mount -o loop win7.iso mpoint
mkdir copy
cp -ra mpoint/* copy/
The loop mounted iso is read only, so we need to copy it first. Now delete ei.cfg:
rm copy/sources/ei.cfg
This is the easy part. Now we want to create a bootable iso image from the directory copy, and here it gets a bit tricky. Luckily I found this very helpfull post. It boils down to extract the boot image from the original iso with
dd if=win7.iso of=copy/boot.img bs=2048 count=8 skip=734
and create the new iso with
mkisofs -o win7_multiinstall.iso -b copy/boot.img -no-emul-boot -c BOOT.CAT -iso-level 2 -udf -J -l -D -N -joliet-long -relaxed-filenames
This should leave you with a new iso image which lets you choose the installation version. Of course, you still need a valid key for that version :-)
