I travel for business quite a bit. But I also want to do some light gaming, especially when I am stuck in hotel rooms on the road. The M1330 is a great choice.
It's very light and portable (13.3" screen, 4.2lbs). It travels well in briefcases and laptop bags because of its size and weight, and travels well in coach (you can open the screen all the way in a coach seat, and you don't run into the problem where the screen may get damaged if the fatso in front of you reclines his seat suddenly). It's GREAT for playing movies on airplanes... great screen, small slot-loading DVD drive, and dual headphone jacks for when you travel with your significant other.
And it's pretty darned good at gaming. I don't know what kinds of games you are into, but I can play World of Warcraft at high detail level at 1280x800 and get ~30-50fps. I can play Call of Duty 4 at low detail level at 1280x800 and get ~30-50fps.
As for battery life... I haven't used the Inspiron 1420, but I can say that I have a 6-cell battery in my M1330 that gets me 2.5-3.0 hours of use, and a spare 9-cell battery that gets me 4.0-5.0 hours of use as a backup. I fly from New York to San Francisco quite often, and have never been in a situation where my two batteries are not enough.
Out of the two, I'd say definitely go with the M1330 for its superior LED-backlit display and its smaller size.