I've been planning on making this conversion myself. And I do plan on setting it in Dark Sun. However, I will be taking many liberties with the original story to make it fit better for my needs.
I plan on running it as an epic tier campaign. And I will be modifying the overall story arc to make the prophecy of Martek and adapting it to be about the resurrection of a long dead god. I figured that since the heroes are of epic level, their actions should have an effect on the world itself.
I had recently adapted the Slave Lords series of adventures into a paragon tier campaign set in Eberron. When I started to convert the first module, I was trying to convert each encounter more or less exactly as it had been written from 1e to 4e. I realized that some of the encounters didn't really seem to make sense. And others just didn't fit. Plus, if I had made each and every encounter a level appropriate encounter, the game sessions would end up taking much longer and the campaign would have stretched out much longer than it did. As it stands, we ran through it in about one year (playing only every other weekend and missing a few sessions due to life getting in the way).
But taking what I learned, I plan on either either eliminating less important encounters entirely or turning them into a role-play encounter. Some of the traps don't translate well into 4e so I will likely make them a skill challenge based encounter. I will also likely modify some of the easier encounters to include a terrain-based or environment-based hindrance to the players.
Personally, I'm looking forward to the last module in the series where the characters will be in Martek's tomb and they get to travel to basically other demi-planes. It should be a lot of fun.
I guess the overall point I'm making is that, in my experience, I've found that it is better to take the overall theme of the story and the general plot line and use that to guide a conversion to 4e because an encounter-by-encounter approach just doesn't seem to work out.
