Here is a simple scheme to upload files from directly within iPhoto. It uses OSX's ability to mount a remote server, as well as ZenPhoto's simple album creation method.
First, connect to your remote server using the "Connect to Server" function from Finder's "Go" menu. Several flavors of connection are supported in OSX, but perhaps FTP will be most common for shared hosting servers. If you want/need a secure SFTP connection, you have to use other means than "Connect to Server". I have found MacFUSE to be very effective. Google "MacFUSE" to learn how to use it. The key point is that you want a server which is navigable by Finder (as opposed to a stand-alone FTP application).
Second, simply use iPhoto's ready-to-go "Export" function to send files to your remote server, using the usual OSX directory navigation dialog when you execute the "Export" command from iPhoto's "File" menu. You can resize photos, etc. at this step.
If you want to create a new album for your uploaded photos, simply create a new folder in step 2 somewhere in your ZenPhoto album structure (e.g., in the "Albums" folder or a sub-folder therein). ZenPhoto will find the new folder and create an album. Then just use ZenPhoto's admin tools to refine the details of the album (title, comments, etc.)
This beats the limits of the php upload. It's so easy it almost obviates the need for a separate iPhoto plugin for ZenPhoto.