For Windows Marketplace, Microsoft's solution would be that the user would not require special hardware (DVD burner) or knowledge (how to use DVD burning software to burn an ISO image).
This means that users that have acquired Vista via Windows Marketplace will not get an ISO file, but three files: VistaSetupPrep.exe (73.76 MB), boot.wim (116.31 MB) and install.wim (2.25 GB). These values are approximate, as they are associated with either the 32-bit or 64-bit editions of the operating system.
So the procedure is as follows:
After all of the files are downloaded, you can launch VistaSetupPrep.exe (or simply click the "Install" button in the digital locker assistant). VistaSetupPrep.exe then extracts the 500+ files compressed inside it and links the .wim files into into a folder called "Vista". The end result is that the Vista folder is a replica of the Windows Vista DVD. Before VistaSetupPrep.exe exits, it launches the setup.exe in the Vista folder and Windows Vista setup starts, just like if you had launched it from DVD(now that's cool right).
But there is also a way to transform the three separate files into an ISO image that users will be able to burn to a disk - So that's exactly what i'll explain to you now. First off, you have to paste all files on C:. Then run VistaSetupPrep.exe in order to extract the files of the operating system. Next, download CDImage, which you will have to track down and download yourselves, for various reasons that I will not get into here.
Now launch “cmd” and enter "cdimage -m -u2 -bC:Vistabootetfsboot.com C:Vista C:Vistax86.iso" to create the Windows Vista ISO image. Next use your usual DVD burner to burn the Vista ISO to a DVD, just make sure that you use the minimum speed.
Hope this helps you out in getting your Vista Installables onto a DVD disk easily!!