I may not have understood your first post fully and I would not want to mislead you in any way. As I understand it, NIS is a collection or 'suite' of programs, that includes NAV, a firewall, Ghost, Disk Doctor etc. I only have NAV, so I have no first hand experience of the other programs.
Are you saying you had NIS 2003 and attempted to update or replace it by downloading the 2004 version entirely or did you only try to update NAV?. If it was the whole NIS program, was it only the install of the NAV component that went wrong or did it all fail to complete?.
As long as you retained the .exe file you got from Symantec and the reference numbers in the documentation which you presumably saved or printed, I believe you are allowed a number of download attempts for a fixed period of time.
If you have used the Symantec removal tools you may be OK although I remember reading somewhere that there isn't a tool for all the 2004 products so that you may have to follow the manual uninstall procedure that you can get from the Knowledgebase. If I can find it quickly I will post a link below.
If the CD option does not cost too much extra, it has the obvious advantage of allowing you further install attempts without a new d/l. Bear in mind that product activation could complicate this slightly but not until you have achieved at least one successful installation (I assume).
Found it! Read carefully but I think it covers your situation;
http://service1.symantec.com/SUPPOR...=2004 for Windows 2000/Me/98/XP&osv=&osv_lvl=