First off, I've never done what you're trying to do. Having said that, it sounds like you're burning 1 image to the dvd and then expecting to burn another. That's not gonna work. In Toast, what you want to do is burn a data cd that has all the separate disk images on it at the same time. To make it easy, just take all the cd disk images you want on the dvd and drag them to a folder on your hd. Then in toast select the "data" tab as the type of disk you want to burn. Then just drag the folder with the images in it to the Toast window. Then burn it. When you open that dvd you'll see your folder. Open the folder, select all cd images and double click. All your cd's will show up on the desktop.
Hope that helps.