Your script will need to have the information in it to generate the NSE's that will get sent to the Altiris server. I originaly tried to use a .bat file but could not find an example to generate the NSE's on the client. I ended up converting the script to .vbs.
I found this to be a good source of information when I created a custom inventory:
http://www.symantec.com/business/support/index?page=content&id=HOWTO10487
Just make sure to update the GUID to the GUID of your custom data class. To get the guid: From the Manage Custom Data Classes, select the custom data class you created and click the properties button. The GUID for you custom data class will be there, and you might want to note the Table Name that you will use to run a SQL query to see your results from the custom inventory.
I also attached the .vbs script from the custom inventory I created. It gathers information from the registry relating to SEP.