bruce_77,
You didn't mention which third party deployment package you're using, so I'm afraid I cannot comment there. However, if you have a properly defined and documented deployment system, you should really stick to deploying the software with that. Mixing and matching deployment will become difficult to track from an administrative standpoint, plus unlike most dedicated software deployment solutions, Group Policy software deployment doesn't really have any substantial reporting capabilities.
If you do use Group Policy, you need to assign the package in the Computer Configuration > Software Deployment section of the policy, and link your policy to an OU containing the computer objects. If you define it in the user configuration area, you will actually have the unintended consequence of deploying that software to any machine the affected user logs into.
Yes, the document you linked to is the correct procedure. You would need to follow the "Assign a Package" section and ensure you use computer assignments, not user assignments.
-Matt
