Sally when we have flown Gatwick/Atlanta via Delta on a 777 we have always had a seat back TV. The 757's not only have seat back TV/videos but inter-plane trivial pursuits and live Fox News. Did you mean 767 flying back from Atlanta/Gatwick? If so that is only overhead screens but I imagine most of your journey will be at night anyway.

We did have our plane changed once from 777 to 767 so it may still be worth taking the DVD's and ipods.
You can also check nearer the time to see what films will be showing at
http://www.delta.com/traveling_check...ment/index.jsp

Do you have allocated seats? It is also worth logging onto the Delta site where you can move your seats if you are not happy with them.