Hi, CBZ9104:
Remember that NS 7.5 only accepts communication with legacy agents if you active LAC (Legacy Agent Communication) that you can find under Settings > Notification Server > Notification Server Settings
At the same time, with 7.5 you need to register the agents on the NS on Settings > Agent/Plug-ins > Symantec Management Agent > Settings > Registration Policies by defining Registration Rules
See the answer from Igor Perevozchilov in this thread:
https://www-secure.symantec.com/connect/forums/altiris-75-agents-not-reporting-inventory-smp-75
Good luck :)