Given the uncertain state of Entourage I'm not sure if this is such a good idea but the option does exist:

Archive Content (from page 45 of the Pocket Edge User Guide)

To archive your content on the enTourage server:

1. Press the Library icon to view the contents of your library. Select the folder for the content to be archived.

2. Select the Checkmark at the top of the library screen to turn on checkmarks. Select the check next to the item(s) you want to archive.

NOTE: You can archive book markups, journals, and other non-DRM content. Your content will be archived on the enTourage Systems server. Each registered user is allotted up to 1G of storage free of charge.