Another “so I don’t have to look it up” post:
Connection dictionaries are the collection of information in your eomodel that configures your access through jdbc to your database.
It is possible to set/modify this information through code and I, along with many others, have built classes that read these settings from your Properties file on app launch. Project Wonder has ERXConfigurationManager that will do this for you as well.
Just drop those entries into your Properties file and away you go. Also, because the ERXConfigurationManager reads all your Properties files, you can override the settings in your project with personal ones in your ~/WebObjects.properties resulting in fewer changes to make when deploying. In fact that little trick works great for er.javamail and log4j settings as well.