Peter,
I would use that latestnis link I gave earlier which downloads a single installation file NIS-ESDND-21.2.0.38-EN.exe -- about 150MB I think -- which you can save and then run after removing N360 without worrying about the installation getting corrupted by internet problems.
If you should have a problem with the KEY -- how many characters are there in it? 5 x 5 char groups is normal -- then I doubt there will be any problem in having WH Smith or Norton CHAT in the UK resolving it for you.
Don't forget the multiple runs of LiveUpdate to make sure you are fully uptodate.