I don’t use InstallShield personally (I use WIX 3.0) and so I cannot give
you much additional help on how to make it do what you want.
However, I can tell you that the latest version of DIFx (including DIFxAPP)
is 2.1.0 (from the Win7 WDK). That is the version I use and have observed
it doing the correct thing when asked to process DeleteDriverFiles=yes.
I do not have any [DefaultUnInstall] section in my Net PnP device INFs or
NetService INFs.
There are no DIFxAPP functions to call. The behavior of DIFxAPP is entirely
driven by the custom table inserted into the MSI package and processed by
the DIFxAPP Custom Action (MsiProcessDrivers or something like that).
It is my strong suggestion that you use the DPINST tool and/or the AppDrv
sample from the WDK to experiment with your driver package installation to
ensure your INF is acceptable to DIFx and that the options do what you
expect of them.
After you get that all put together, then figure out if IS2008 changes the
behavior and then how to compensate for it.
Good Luck,
Dave Cattley