Symantec Management Platform server logs (a#.log) are stored here:
SMP 7.0: Program Files\Altiris\Notification Server\Logs
SMP 7.1: ProgramData\Symantec\SMP\Logs

Note: ProgramData is hidden by default and you may need to "Show hidden files and Folders"

Symantec Management Agent logs (agent.log) are stored here:
XP/2003:  Program Files\Altiris\Altiris Agent\Logs
Vista/Windows 7/Server 2008: Users\Public\(Public) Documents\Altiris\Altiris Agent\Logs   OR

Vista: C:\ProgramData\Symantec\Symantec Agent\Logs
Mac: opt/altiris/notification/nsagent/var/aex-client.log

If agent logs are not found in the above locations, for Symantec Management Agent  Version 7.1 SP2 on Windows 2008 R2/Windows 7 clients (including the notification server) environments check: ProgramData\Symantec\Symantec Agent\Logs