I have been researching this for over a week now. I've tried a few tutorials on custom rewrite rules and custom post types, but I'm still not sure which direction I should go in for making this happen. And it absolutely has to happen. This is a large client who needs to retain the same link structure that is coming from a moveable type envrionment:
WP ---> http://www.domain.com/pastissues/category/here-is-the-postname.html - works on wordpress
MT ---> http://www.domain.com/pastissues/multiple-word-category-orsingle-one-here-is-the-postname.html - works on Moveable Type
/pastissues/%category%-%postname%.html --> this produces the right looking link, but fails when I request an article if the article has a category that is more than one word.
So I probably need to write a custom permalink plugin. I've tried looking through available plugins out there, but custom permalinks won't help me, because I'm a multi-site install.