Hi Dedicated,
It sounds to me as if this is a Vista issue, not nortons really mostly because its a download issues not uploads that your having, so I would suggest you have a look at this thread,
https://forum.winmxworld.com/index.php?topic=4804.0.htmlMake sure any folders your files download to have this and so does the WinMX program folder as well. Make sure that your folder for incoming files is an actual folder and I would suggest putting it on the root of the drive like C:\Downloads. Also it may be a good idea to start fresh rather then try to complete files you have partials of, maybe a small corruption in the files that are incomplete along with the Vista permissions issues.
Btw, 2.6 has been tested on Vista and does infact work if your still wondering that.
Im not a Vista expert but just thought this sounded like it may help.
Let us know.