Been awhile since I tested VSO DivX to DVD. What location did you specify for it to put the converted files? There should be a folder called VIDEO_TS that you can open in DVDShrink. It's actually useful to do this, since if Shrink can open it, you know the authored DVD is compliant and will play okay on a standalone. Now, if you are pointing Shrink at your original DivX, that ain't-a-gunna-work.
Do this: Load your DivX in VSO DivX to DVD. Leave the defaults alone. Convert it and take note where the output files are going. Simple.
From here you have several alternatives:
1) Hit open files and load the VIDEO_TS in DVDShrink. Hit backup in DVDShrink, specify that it create an ISO and burn with DVDDecrypter. (Get it here: http://www.mrbass.org/)
2) Get ImgTools Classic to create the ISO from the converted files, get it same place as above. Burn with DVDDecrypter, ISO Write mode.
3) Get a freeware burner somewhere, off the top of my head I'm sure Deep Burner can do the job. There are some free burning apps in the tool section at http://www.videohelp.com