After getting some reports of issues with dasBlog I've moved across to SubText which so far seems nifty. The binary version didn't work for me so I built it from source but had an otherwise trouble free install. This tool exported all the content from dasBlog except the images (which I solved by just leaving the images where they were). I also found this post from Ayende helpful in getting the post ordering sorted.
In theory I've tweaked things so that the URLs should be the same for older posts. The RSS link has changed but Feedburner should mean that's not an issue for most people.