Yeah it'll run on 256, but that doesn't mean it will run well

You absolutely will need a 1GB swap for that.
I wouldn't pay much attention to the Dell website with regard to Linux. They aren't the sharpest folks around when it comes to Linux. What is this driver supposed to be for?
I'm not familiar with Maxthon so can't comment there. I get the impression it's just a Netscape clone. Hell, even netscape would probably perform better on that system than FF, but Opera has plenty of features without as much overhead.
You're welcome, happy to help. For that machine you might even want to think about trying out Slackware Linux as it runs quite well on older machines and comes with Fluxbox in the default installation. In Ubuntu you don't want to use their Fluxbox package as it's behind development quite a bit and is pretty crippled. You'll need to download and compile the development release if you go that route.
Any questions related to Linux just let me know.