How to make previous versions available for users?

I am new to using subversion, trac and do not clearly understand how the wordpress plugin repository works. When committing WP Responder I put all the files in a directory called “trunk” and committed it to the server. It worked.

It may be useful to make previous versions of the plugin available for download. So I copied all the files from a previous version (4.9) as well as the current version (4.9.5.1) and placed it in the “tags” directory of the repository.

So tags had two directories: 4.9 and 4.9.5.1. The 4.9.5.1 had the same content as the trunk directory. When I did this the downloadable archive had only the php files directly under the trunk directory and not the sub directories that are part of plugin.

So I had to removed all the directories within the tags directory to restore it to the previous state.

What am I doing wrong? How can I make previous versions available for download?