Battery life really depends on what you do with it. I bought a laptop that gets shit battery life... just over an hour... but I NEVER use it far enough away from a powerpoint for it to bother me. If you're THAT worried about it, buy a second battery.
It doesn't really matter what processor you get, just be sure to it's a Core2 Duo. Other than that even the base models are quick enough these days to do the regular plodding (music, video, + general internet trolling). That being said I'd look for something with at least 2gb RAM as it'll let you do more things at once without noticing the slugs and it also helps when you're watching movies.
I bought a Dell Inspiron 1501, it's one of the basic models. It kicks ass. Unfortunately though I got the AMD so it's a bit sluggish, but other than that I've never had a problem and TBH I don't run it hard enough to notice the slugs too often anyways.
These Dells would be good to look at. They're basic and pretty cheap... the $999 one looks really good, and it comes with 2gb RAM and a 160gB HDD... I would take the upgrade to the Core2Duo and the TrueLife screen.
The other thing I'd suggest is to either get it with XP SP2 on it or buy it as-is and when it arrives, format and install XP SP2. Vista is still a bit shaky... I'm a bit biased though, I REALLY don't like Vista