Dual databases

[Admin]

If you are using the same user/pass for the two databases, it's really simple actually.

All you need to do, is first move the attachment table from one db to the other.
Then, find all places where you have SELECT [...] FROM attachment, and change that to newDBname.attachment (also do that for JOINs with the attachment table).

The places I can currently think about are:
showthread.php (where you select the posts there should be a reference there to that table)
attachment.php (duh)
functions.php (acceptupload() is the function that actually adds the files to the database...)

Good luck.