You can get the plugin easily using the Eclipse Update Manager, just click Help→SoftwareUpdates in Eclipse. The Eclipse Update Site for ABL ODA Data Source is available at this URL:
http://www.ganimede.ro/birt.oda/update
If you are not familiar with getting new software and updates to Eclipse, please read this article.
If you have trouble using the update site then you can download the plugin jars and install manually from here: plugin directory.