The MsiProperty element is used as a child of the MsiPackage element in a Bundle. The Burn engine will resolve Variable references Value attribute of the MsiProperty element allowing install time changes to be passed to the MSI package.

In the following example the string bar is always passed to the MSI via a Property named BAR:

<Bundle ...>
  <Variable Name='Foo' Value='bar' />
  ...
  <Chain>
    <MsiPackage Source='path\to\your.msi'>
       <MsiProperty Name='BAR' Value='[Foo]' />
    </MsiPackage>
  </Chain>
</Bundle>

This example isn't terribly interesting unless there is some code in the BootstrapperApplication that modifies the Foo bundle variable at install time.