vB API question

[obscureclouddon]

First of all I'd like to know if I am using the API for something that it is intended for (or possible nonetheless).
I am trying to utilize the API to log users into my vB installation when they log into another part of the site. That is, I want them to seamlessly be able to navigate an existing wordpress installation (with 15k existing accounts) and the newly installed vB forums.
I have ported the accounts over already. That is not much of a problem (except for the passwords....)

Now I am trying to set it so that when they log into the WP, the API logs them into the vB.

Will this work?

Is there a better way to get the desired result?