Windows should have an FTP client with it.... You would need to know the FTP site name or address for NC and then determine whether they have a public anonymous FTP uploading directory for maps....
Generally, the syntax is (at a DOS prompt):
ftp nameofsite
where "nameofsite" is NC's public FTP site.
Once there, you'll see a login prompt (and it would hopefully say that "anonymous logins" are okay. You would then enter "anonymous" for the username and your email address for the password. Then if you get that far, you can usually do either a "dir" or "ls" at the prompt to see where you are. Often you'll see a directory structure that lists something called "/pub". If you do a:
cd pub
then do a dir, you may see directories that say "uploads" and/or "downloads", plus other directories for various things. If they have an "uploads" directory, you would then need to use the command that will copy your map from your machine to their machine. Also you need to make sure that the "mode" of copying is "binary" (because your map is not just plain text". So at your little ftp> prompt, you would need to type:
binary
Then try typing:
put c:\pathwheremapis\nameofmap.unr nameofmap.unr
(where there's a space between the "c:\pathwheremapis\nameofmap.unr" and the "nameofmap.unr") - basically you're copying your map file to a file that will be created on their machine, which will keep the same name as your file - you have to explicitly tell it that.
Again, this all depends on whether they have something like that setup.