So the new image you just created was based on the exact same set of files?

As for getting me 5mb of the image, put the dodgy DL in the drive, go into 'Read' mode and create an image of it on your hdd. Then you can use a hex editor or file splitting program to get 5mb from the start of the image.

You can also use IsoBuster (which you've already said you have). Right click on the top level item in the treeview on the left (probably says DVD or something) and then click 'Extract From-To'.

Select the 'Length' option and type in 2560.

Then select 'User Data' and click 'Start Extraction'.

That should work direct from disc or from an image file.