This is pretty easy. The "Features" page uses a subclassed container
(the code for those checkboxes is in helpers\comctl.c, but
this you need not worry about). All you have to do is take a look at
src\shared\xsetup.c. The setFeaturesInitPage
function is responsible for initializing the container with the features,
while the setFeaturesItemChanged function reacts to selection
changes in the container.
To add something, perform the following steps:
include\dlgids.h, where all the
other items of this kind are (search for ID_XCSI_GENERALFEATURES
to find them).
001\xfldr001.rc), using that ID.
FeatureItemsList array in
src\shared\xsetup.c. Your item will then automatically get
inserted into the container by setFeaturesInitPage.
setFeaturesInitPage, you need to add a line
which checks the container checkbox according to the setting (those
ctlSetRecordChecked(hwndFeaturesCnr ... lines).
setFeaturesItemChanged, add a case/switch which
reacts to user changes.