Programs you will need:
ZXBTools 1.6a
DVD Decrypter (Ultra ISO will do too)

Since pictures explain a whole lot more, and save me time, I will do that.

Note that this method can be used for 1 game too.

First, have the iso's you want to add to multi disc iso.

1)Now, run the ZXBTools.

2)Have the same settings as mine

3)You will be moved to this menu, have same settings as mine

4)Click ISO tab, and press EXTRACT if you have an ISO.

5)Press "add xISO", pick directory to which you would like to extract the game to. After that, press "extract"
(While extracting, you can press "background" so it doesn't bother you, it will pop up back when it's finished)

6)After that, press ok. Now you will be back in to the menu, press "add directory" and add folder to which you extracted ISO. This is how it should look

7)Press next. You will be put to one of the games you added, and you can pick cover for it as well as short description.

Now pick the theme you want, and have same settings as mine. (Press preview to see how will menu look in xbox)

Create an ISO. This will take some time, so go call your family or watch episode of boondocks.

9)OK, now that we are done with that, close down ZXBTools. Now run DVD decrypter.

10)Press Mode tab, and pick ISO>WRITE. Menu should change, so change write speed to lowest.

11)Pick the ISO that you created with ZXBTools, and burn it to a dvd. Lengthy process, so go eat something

And you are done. Multi-disc is ready. Go now and don't waste a goddamn dvd on a 50mb game.

Couple of notes:
Maximum amount of multi stuff is 15
Sometimes you get error that iso mode is not 2048, easily fixed by re making an ISO
Don't fill up disc completely, leave at least 10mb or so, or else menu won't work. Disc will still run, default menu is sucky
You can't do multi disc to a DVD9.

This is how burning games started for me, so I felt like this needs to be put here.