When dealing with a client recently who has Software Assurance, we went to download their updated software as per their SA Agreement.
Here is what we ended up with:
Okay, the file's label says, "ISO", but the actual extension is .IMG.
Seems that one need only RENAME that .IMG to .ISO and away we go! :D
Burn The ISO to disk, and then go ahead and run the software install/upgrade.
Thanks to the TechNet Forums for this one (You will be asked to create an identity for the forums to view this link).
Happy with Software Assurance!
Microsoft Small Business Specialists.