Is it possible to connect to a mysql database from an other site which is not allowed to see the password, like to have a portal and then offer some open-source mini portals to collaborate with yours.

Any ideas?

store the password as a MD5 hash? Else here is a way to call a php file from another site:

<iframe src="http://www.x.com/test.php" frameborder="0" scrolling="no" "width=100%" height="100%">
</iframe>

Couldn't you just set up a user in your database 'anonymous'@'%' with no password? And make sure that user doesn't have too many privileges...