How to change options of Superdrive to dual layer


hey guys. i downloaded toast 7 titanium, inserted the blank DVD-R did all the bits i needed to do in the program (selected the video_TS option and folder etc) but every time i click record, it just shakes, like ive done something wrong. the date will fit onto the DVD im using, and my G5 Imac does have a dual layer supported DVD writer drive. i can burn (eventualy) using the built in burn folder options of tiger, but then its not set to duel layer. so, 2 questions there really. if toast doesnt work, how do i change the built in burn options to dual layer, OR , what am i doing rong in Toast?