Stuart Lewis has released a PHP library for the SWORD (Simple Web-service Offering Repository Deposit) software.
Here's an excerpt from his post:
There are many web applications that could deposit into repositories using SWORD, and many of these are written in PHP. Examples might include open source Content Management Systems, Blogs or Wikis. By using this library you can easily retrieve service documents and make deposits by using the API provided. There are two simple method calls (one to retrieve a service document and one to deposit a file). In addition there is a packager included that can package a file and metadata together into a package format supported by both DSpace and EPrints. This is the same code which is used to power the Facebook SWORD deposit tool (http://fb.swordapp.org/).