You need to use a registry editor to dump the entire registry to a text file. Then install the cab quickly, then immediately dump the entire registry again to a separate text file.
Then bring those files over to the PC and use WinDiff (or equivalent compare app) to find the differences between the two files. Some of the entries you will want to ignore, the rest are the changes that the cab and/or its setup.dll made.
It takes a lot of trial and error... that's why we hate setup.dlls so much
