My subdomain is setup with / which of course needs to be the folder where your Zenphoto is. If it is in a folder it runs also directly in the root btw.

But my main domain does not link there, too, and I actually never tried that. I guess I can't answer that currently.

Sorry, zenphoto can only occupy one place at a time. It depends on the WEBROOT for its addressing. You can have it run from your subdomain or from your main domain, but not both because the rewrite base will be set for either one or the other.

Oh~ I didn't know I have to first check it in the Admin Options to enable mod rewrite.

I noticed that the modrewrite changes
http://gallery.myurl.com/index.php?album=ETC&image=PB120009.JPG
INTO
http://gallery.myurl.com/ETC/PB120009.JPG

Is there anyway to discard image name? And only put the album name.

Make it something like
http://gallery.myurl.com/ETC/