From jQuery JavaScript Library

Subversion (SVN)

All source code is kept under Subversion control, which you can browse online. There's a download link available for any file or directory, if you only want to download a portion of the jQuery UI code.

If you have access to Subversion, you can connect to the repository here:

svn co http://jquery-ui.googlecode.com/svn/trunk

You can also check out a specific version of jQuery UI from subversion at:

svn co http://jquery-ui.googlecode.com/svn/tags/<version>
e.g. svn co http://jquery-ui.googlecode.com/svn/tags/1.5rc1

Commit Access

If you need commit access to the jQuery UI subversion repository, post a request to the jQuery UI Development list.