But I recommend do it offline because you also need to replace modded mum files with unmodded ones in C:\Windows\servicing\Packages after installing it using Windows 8.0 DISM
There is some script to install but i don't know who made it and it installs PS 3.0 in online OS in one click without problems
Also to install PowerShell 3.0 on Vista you need DISM from Windows 8.0, but it can't work with online Vista installations
I had some problems with dism commands. I managed to mount the image but couldn't add the packages due to a read only error. I was trying to do 5 packages at once though before I saw your message. After that I tried with one package with the same read only error. Then I unmounted the image successfully(?) and tried to remount it but it was say that it was already mounted although the folder where I had mounted it was now empty.. Anyway I will try again tomorrow.
You may create a VHD file by pressing Win+X+K , and then set the appropriate options, decompress the .wim image to the mounted .vhd drive, then you can have a try. e.g. DISM /image:F:\ /add-package /packagepath:...../,,,.cab or ,,,.mum or ,,,.msu. Or, create a VM with Oracle VirtualBox, select .vhd as its virtual disk. (VMWare doesn't support .vhd )
So I tried again and it is the same problem again. "Error 2: Unable to access the image. Make sure that the image path and the Windows directory for the image exist and you have Read permissions on the folder." All my folders are marked read only and apparently this is the default behavior for windows 7. When I untick the read only and saving the changes the read only becomes again active on its own. Going to do a fresh install of 7 and see if this is the default behavior on a fresh install.
https://forums.mydigitallife.net/th...s-vista-sp2-64-bit-beyond-its-eol-date.83461/ , Step #23, this may help.