register into 2 db's at once

[dimava]

ok, here's the deal:

I have 2 databases that are under the same u/p
both databases run vbulletin 2.2.8
Each database is for its own site

I need to make it so when someone signs up at one site, it automaticly adds their usergroup, username, password, and email to the other database.

What would be the best approach?

thanks,

Dimava