Altiris works the other way round. Create a Software Resource for the .NET 4.0 install with a default install command line and ideally a detection rule.
Create a Software resource for the other application and, from the Associations tab create a dependency on the .NET 4.0 resource and save. (If you now look at the .NET 4.0 resource you'll see that the other application shows as depending on it.)
The right click the other application > Actions > managed software delivery. Step through, including the 4th step and you should be able to select the .NET 4.0 resource too.
When the Managed Software Delivery Policy runs on a machine it will install .NET 4.0 first, only if its not detected if you have a detection rule.
For more info see my article:
https://www-secure.symantec.com/connect/articles/software-management-framework-quick-start-itms-71-sp2