How do i tell my computer to use my external disk-burning drive?

Can anyone please tell me how to tell my macbook pro (tiger os x 10.4) to read my new Lacie external dvd/cd-burning drive in order to burn a dvd, rather than the current internal apple one (which came with the mac upon purchasing and recently went kaput)? btw, I CAN see this Lacie's name-path when I go into the apple-icon's "about this mac/more info". Then, I can see the lacie drive's name-path either by accessing the Hardware's option of "FireWire" or "Disc Burning". That's the gist that I can figure out right now--nowhere are there instructions for SWITCHING the disk-burning drive in order to burn dvds (i.e., nothing telling me how to instruct my computer to read this Lacie drive for burning dvds, rather than the internal apple drive!). I know it's gotta be an easy switch, but I'm just not finding the instructions. Thanks!