julandy-
as a dreamhost user myself, it makes much more sense to segregate your zenphoto DB from other DBs. on dreamhost, you can set up many MySQL DBs, so you don't have to worry about limitations. that way you don't have to worry about mixing prefixes,etc.
so what i do, is have a wordpress DB, and a separate DB for zenphoto. it's just easier that way.
However, if you do want to continue to use the prefixed DB, you should nose around in the zp-config.php file. Look for:
`// If you're sharing the database with other tables, use a prefix to be safe.
$conf['mysql_prefix'] = "";`
in the code, and set that to your prefix.