My oldest daughter was 5 when my youngest was born. She asked if she could be there when I had the baby. So we watched videos (the ones mentioned, I think, plus some others my midwife had {I wish I could remember the names of those}) and Baby Story on tv. She had no problem with those. We warned her that when mommy is in labor, it hurts so mommy will probably make some noises that she doesn't normally make.
Also, since labor can be an intense time (fortunately, I ended up laboring most of the night and she slept thru it), I had her grandma there for distraction. When we thought birth time was close, we woke her up. Unfortunately, it wasn't, so she saw some pretty hard labor for a couple hours. But, like I said, we had her grandma there for distraction. They made cookies (home birth) and played games.
When the time came, she had the option of watching and we made sure, if at any time, that if she was uncomfortable, that she could leave with grandma. She didn't have to watch. She ended up watching the whole thing, she wasn't TOO close to the action. Afterwards, she said she didn't know there would be so much blood, but it didn't scare her, since she had seen the videos. She also got to hold her sister just a few minutes after birth. I think that reward made the whole thing positive too.
I think if you prepare him and give him the option of leaving at any time during the birth, then its a great idea.