Hi, I am running nginx/0.7 + php/5 (fastcgi) + mysql/5. I don't need SEO friendly URL, so URL rewriting is disabled.
I want to run the core zenphoto system on mydomain.com, and I want the actual photos to be served from subdomain.mydomain.com. Can this be done? I have tried storing the albums folder external to the main zenphoto folder, but all the images are still served from the main domain.

Not really sure what you are asking here. You want the url of the images to be subdomain.mydomani.com/something? I think you would have to have zenphoto running from the subdomain for that.

I want to run zenphoto from www.mydomain.com, but I want to serve the actual images from... say... media1.mydomain.com, media2.mydomain.com

In other words, zenphoto is run by the httpd on mydomain.com, but the images reside on the media[1..N].mydomain.com subdomains, to which the zp code will link.

I am planning to launch a large gallery with zp. so spreading the contents across several subdomains for scalability.

I think there are some image/file hosting services that take this approach... i.e., the main domain hosts the PHP code, but the actual files/images are distributed over several subdomains.

Do you mean by different servers? Just having different subdomains (without different servers) will not help any performance problems. Anyway, zenphoto has to be able to access the image files. It is not a distributed application.

If you really mean several servers please see here http://www.zenphoto.org/support/topic.php?id=2908&replies=2