Ok so, my friend had recently only got zenphoto and he liked the plugin so he took it and made it work for wordpress 2.3.3+, including 2.6.2 and probably even 2.7. He said that he won't take over the project or anything at all but, he updated the plugin anyway.
What's different about this plugin from the original is that, all you need to do is upload and activate the plugin and you're done. There is however, no menus or tabs to find this plugin in wordpress, it just simply does its thing by using cookies.
The only requirement is that you need to have the same username in both wordpress and zenphoto but, not the same passwords and it will just log you in automatically with you login in wordpress.
Here is the link for it(label this as unofficial 0.3 I guess):
http://www.mediafire.com/file/ixnmamyggyu/zenphotosinglelogin.php
If its against the rules to put links of files from other locations or I needed consent first, please delete the link.