I do most of the map design in ArcIMS directly, it gives you finer control. There are somethings you can only do there (I think) as well, such as rasters and SQL queries. I do some fundamental parts of the map design in ArcIMS Author or ArcExplorer, and then the rest by hand in a text editor.
I have never tried a conversion script, and I wouldn't want to play with that anyways. ArcIMS only supports a limited subset of the cartographic features in ArcMap.
It is a bit time consuming, but when it is up and running and you only need to tweak it, it works very well.
ArcGIS ArcMap Server is an extension or part of ArcIMS, introduced in 9.0 (or was it 4.1?). First it was windows only, but not it runs on all supported platforms (I think). I haven't played with it yet. It gives you access to all the functionality in ArcMap through a server, but I am quite sure you lose quite a lot of performance on the way as well...