I've been posting like crazy about this issue here & not solved it so I thought I'd offer to pay for help.
I have a Typepad blog which I'll be closing down. I've imported all my TP posts into my new WP blog. But anyone who uses old TP formatted links (with underscores & html) will be forwarded to my WP blog, but will not reach the actual post because I haven't been able to create a rewrite rule that would convert the old link properly to the new WP formatted link (with hyphens).
If you're experienced with htaccess & mod_rewrite, pls. contact me here or via my blog & send an e mail.
I'm losing half of my old site's visitor traffic due to old format links which are essentially dead & I'm tearing my hair out about it.