iDVD only works with Standard Definition (SD).
You shot your video in HD (1080 i or p), down-converted it to 720p (?) with the .h264 codec (bad codec for editing purposes) and then edited the video in FCE with a resolution of 720x480?
720x480 is the SD resolution of NTSC DVDs.
Why the need to convert the video from SD to HD (720p) to bring it into iDVD, which will ultimately convert it back to SD?
Just export the final master of your edit as a QuickTime (.mov) file with the Apple DV codec for example.
.h264 is not the best choice for such purposes.
In the end the video on DVD will be compressed, so to get a good result (image quality) it's best to not compress to often.
As a user on this forum once said: See this empty soda can? Throw it on the ground and jump on it to make it as small as you can. When you have done that, pick it up and form it back the way it was as good as you can. See how it looks now? - That's compression.
I was paraphrasing.
Also please use more coherent sentences next time, as it is hard to understand what you definitely mean by the poem you wrote.