|Per-Machine (all user) Installations|
Per machine resources are those that effect more than one user and include "HKLM" registry and "Program files" directories. See "system folder properties" for locations Windows Installer defines along with some sample values.
Unlike per-user installs the software will be visible by all users using the Add/Remove Applet.
You may need need elevated rights to complete the installation (administrator etc), for example if "c:\program files" is read only).
|Per User Resources (HKCU etc)|
If your msi installs any per-user resources (files, registry etc), then you should read the "Per-Machine Installations with some Per-User Resources" section.
If you have any influence with the developers of the product try to get this functionality moved into the application, this would seem to be a good way:
This also allows the installing user control over what those default options are.