I believe it can be done with a program called 'Apache 2.0'. You can start your research here: http://www.ps2nfo.com/.
I think people were converting dvd9 games to dvd5, but i'm not not totally sure. Think is something i copied from a forum post at this site: " 1. Use a tool that can view both layers of a DVD-9 image, such as Apache 2.0, to extract both layers to the . (In this case, it is mantadory to use the folder. Under normal circumstances, Apache 2.0 will create the NO_LABEL folder by itself.)
2. Plug the IML file for each disc into dvd iml2iso 4.01, and click Start to build each image.
3. The final size for each ISO image will be as follows:
* Disc 1: 4.31 GiB (4,631,035,904 bytes)
* Disc 2: 4.25 GiB (4,565,893,120 bytes)
4. Record each ISO image to a DVDÂ±R and enjoy. " I was right in that its being done to a game (whose name i deleted) I hope this helps but i have never personally done this.