If you check the liveupdate log (C:\Documents and Settings\All Users\Application Data\Symantec\LiveUpdate\Log.LiveUpdate), there may be some indication as to why it's failing (proxy authentication required, etc). However, this is a very, VERY old version:
"Symantec Antivirus 8.0 reached its End of Support Life as of November 30, 2005 and Symantec Antivirus 8.1 reached its End of Support Life as of January 31, 2007, as defined in the
Symantec Enterprise Technical Support Policy. Therefore virus definition updates are no longer supported for this product."
Thanks,
sandra