User database replication with another site

[rleague]

I'm setting up a content partnership with another site and one of the things we want to do is pre-register users in each other's databases.

I will use my vBulletin forums database from my side. They have a standard SQL database on their side.

In short, I want to be able to extract my vBulletin user database (username, password, email address, name, location) and send it via secure FTP to their server, and download a similar file and load it into my vBulletin user database. I'll build scripts outside of vBulletin to do duplication detection and data cleansing as needed.

So, how do I extract user database information and load/register new users in vBulletin? Is there a mod/plugin that already does this, or am I building my own. I'm more than happy to do it as the SQL layer without using vBulletin functions, or alternatively include vBulletin code and use vBulletin functions in a custom PHP script.

Any tips?