One approach I find useful is, before I go anywhere near Altiris, is to try and silently install the software on a test machine. Once I have got the fully silent install completed I run a one off full Inventory on the test box and then import the Software into Altiris, making sure I add it to the Software Component that Inventory will have discovered.
This saves having to edit the package later if I end up having to create an msi transform or silent ini file or similar.