Hmmm..not sure. I've never downloaded .iso files. I've always just downloaded the files from their website. I could've sworn that literally every software update was listed, but you may be correct in that moving from 7.6 to 8.x is a full upgrade, which would not be on the update list.
As for the install...try these couple of things:
1. Find the .exe file instead of using the autorun and install it from that.
2. Move all the install files onto your hard drive into a temporaray directory somewhere. Then try the install from your hard drive.
3. Move all the Install Shield files to your desktop then try the install. You'll find them in a couple places: C:\Program Files\Install Shield and C:\Documents and Settings\User Name\Application Data (substitute the name you use for logging on where I put "user name"). You can also just do a search for Install Shield, then go move all the files. If the install works...move them back to their original locations. Be sure to note what the original location was!!
Beyond those tricks...I'd retry the download. It might have corrupt files in it...or try re-burning the .iso with different burning software, since the .iso spec isn't real tight and different programs might read files differently.
Hope that helps.
Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com