Sorry, didn't notice the private message ... shoulda just put it in the newsgroup. They don't email me these like they do the replies to the thread, don't know why.
There's two ways.
In Iso-write mode, there is a little icon of an open book in the lower right corner (under "settings"). Click it, you'll see "Change Book Type". Select your drive, select your media type, and pick DVD-Rom from the drop down box. It should say "success" if you did it right.
Also, from the menu bar, you can pick "tools/drive/change book-type".