Same Server / Different Sites / Sharing database

[Logan70]

Is there a way to share the database and run it on 2 different sites working on the same server.

I am running 2 similar sites, but they are specific to different parts of the printing industry.

I want to be able to share the same database (and not for vBulletin), so people can use the same logins and priv information and not have to register twice.

I was thinking that making host not say 'localhost' would work, but that caused errors. Did I miss something? Is there a site ot server setting needing change?

Any helpwould be great.

Thanks