because ESET wants the registered username/password before you can download an update. Trial users of NOD32 is the one that can download the defs without username/password and still need internet access.

Their suggestion is connect your PC to another internet connection (sharing internet access) to get the defs.
http://kb.eset.com/esetkb/index?page=content&id=SOLN308&cat=UPD&actp=LIST

It's been years since I last have NOD32 so no idea if they have manual updating now. You can try to check in their official forum:
http://www.wilderssecurity.com/forumdisplay.php?f=15