Andy Fragen developed a tool for radio (on his Public Tools
page) that extracts all posts out into individual files that are a bit
more intuitive than the radio root file export function.
I've taken the result of that and ripped it with the perl script I just hacked together (0.1 version retrievable here) to get a decent baseline cut of files as expected by a vanilla (i.e. no plugin) install of Blosxom.
So far so good. There are bundles of features to add to the script, especially as I add plugins to my install.