Notification Server 6:
Officially, the 6.2.1302 build of the NS Agent and Inventory Solution for Macintosh do not support the Mac OS X 10.5 (Leopard) platform.
As of December 2009, an official hotfix has been released that provides support by the NS Agent for Macintosh, version 6.2.1302, for 10.5 and 10.6. Please see the following knowledge base article for more details: https://kb.altiris.com/article.asp?article=50717&p=1.
Without this update, please note the following:
Workaround: In the 'Install Altiris Macintosh Agent' screen, highlight a 10.5 machine and click the 'Install Settings...' button. Scroll to the bottom of the 'Connection and Authentication' window. Select the 'Manually select OS type' radio button and select 'Mac OS X 10.4 (x86)' from the drop-down list. Click 'Apply'. The OS version checking logic of the push installation will be bypassed and the 6.2 agent will push install to a 10.5 client.
Notification Server 7:
Notification Server 7.x officially supports Mac OS X 10.5 (Leopard).