Thanks Dim for the response.
I was getting rather desperate as my site was off-line until the comments were back up and I have given up on IntenseDebate. So, as usual for me, it was a case of create a solution with what I have (do the best with what you've got) - this is a bit hap hazard but it might help others as inexperienced as me who are in need of help.
I went with Jcomments - after inspecting their SQL schema, their's was the one most like ID's. I think however that the process I used would work equally as well for Compojoom (might have to fix up an extra table).
After noting down the SQL table specifics, I took the dump file from ID and copy/pasted it into WORD (yes, MS Word). There using find/repalce I removed all the coding ("<[CDATA(... blah blah blah)) and replaced it with neat simple refs per line like "ID, PARENT, TEXT, IP, NAME..." etc. Each ref was on a new line with a tab between the ref and the data. Then I removed all the excess para-breaks on the "text" line and replaced them with "<br />". Then all the strange coded formats "&lqu;" etc. and replaced them with their real chars. Then I escaped the apostrophes with find/replace. I added a "XXNEW" ref line before each record.
Then I copy/pasted that to excel (yes, MS excel). There I wrote some VBA to take the data from the now modified ID dump and convert it (line by line) to the Jcomments table structure and simultaneously add the SQL "INSERT INTO" grammar.
Once that was done... I copy/pasted the output into phpSQL on the server and loaded it up... I had all my comments back with everything as it was, including voting, and all in perfect order (nested)! It took half a day all up but it did work.
It is a very indirect method but it did work. Just be careful of the user IDs (where in doubt set to anonymous (JComs = 0)). I liked using word and excel because it gave me a visual interface with the data - I really need to see it to fix it and it used simple tools I'm really familiar with.
Anyway, I hope I don't sound like a complete idiot - I'm sure their are faster ways but without doing weeks of research I am not able to do them - this used what I had to get the result.
This process might work for Compojoom too - if you have IntenseDebate you might adapt this procedure. MORAL OF THE STORY: As always with anything IT, THERE IS ALWAYS A WAY!