multiple user accounts with duplicate accounts and 60+ posts in each -- any automatic way to merge?

Hi- hoping someone can help.

I have at least two and possibly up to 10 wordpress users with multiple accounts (with the same username and email, but different userids -- I didn't even know that was possible!) as result of importing users with this plugin, from Joost's to a newly-imported blog within an existing network.

Some of the duplicate users have 60+ (different) posts on both accounts, so manually changing the user on one side's posts and then deleting the empty account isn't an option, need something programmatic. I'm pretty non-technical but get my hands dirty. Help?

cheers,
David
PS crossposted here.