If this was your dialog entry for your dropbox(ini sections):
combo 141, 20 140 130 85, drop, hsbar, vsbar, tab 1
and the entry for your ini section contents:
list 142, 200 140 130 85, hsbar, vsbar, tab 1
selecting an entry from the dropbox 141 would populate the listbox 142 with this:
on 1:dialog:yourdialog:sclick:141: {
dir -r yourdialog 142
;loop through your ini and add the %data to the listbox
did -a yourdialog 142 %data
}
NOTE: there maybe errors in this, I havent tested it (off the top of my head)