Welcome to Windrivers Rachel Erica

As you have discovered there are many formats for video... even AVI is only a file extension, one AVI may not be the same as another.

On top of that you have 4 different DVD formats
+R
-R
+RW
-RW

RW's are useful in that they can be erased and reburned a few times...but it depends on your DVD player as to whether it can play them. Most players have a few gotchas when it comes to what burned media they will actually play.

So what make and model is your DVD player?
And how did you create these AVI files - are they from a camcorder?

Edit, forgot about Dual Layer... so what DVD media are you using?