Before I go blundering around deleting/moving directories and files in an attempt to tidy up my hard disks is it true to say that:

All I need for my website/s to work is the relevant .vnu and the _website folder of the same name?

Is there anything else I need?
Apart from of course the relevant CC programs used to make the website in the first place.

If I move .vnu and _website folder to a different partition will that create any possible problems?

thanks in advance

Your going to need everything you added to your site because the vnu is going to look for a file at the location it was originally added from. Example: You add a picture to your page using the image tool. Lets say the image was in a folder on your desktop. When you publish with VSD it's going to look at that folder for any changes made to the file. This is why if you go and move things around you may get an error from vsd stating it can't find a file.
I always recommend to keep a folder just outside your sitename_website folder that vsd creates to keep all the files you add to your webpage designs. This will insure it's easy to find the files later for backup or editing.
Instead of moving the .vnu and _website folder, save your website to the desired location. You will only have to copy the folder with all the files you added to your site manually.

OK thanks for that Rolly.
I have a folder with MOST of my files in, if I move the other files in I realise I will get an error from VSD but will VSD then allow me to put in the new path to the required file?

Yes when you close the site and reopen it it will ask you if you would like to locate any missing files. If you move stuff around with VSD still open and go to publish VSD will error out on missing files asking you if you still want to publish your site.