Coding oermalinks

Hi,

I have developed a theme with regional custom post types and need to rewrite the permalinks to match the current urls on a few hundred posts. I have been snookered with this all day. I have a custom taxonomy called region and each post name / title is the name of a town in that region. How do I rewrite the permalinks to be domain.com/region/town.html eg domain.com/taxonomy/post_title.html ?