It seems that ant dependency management isn\'t great to say the least... But, is there hope? Today there are better choices for build or project management such as maven, iv
I've been using Ivy for the last 4 years (way before it joined Apache) and haven't had any regret.
Without knowing much about your Ant files, it's a little bit difficult to give a definitive answer but I guess that the projects are build in one go. This means that they can't individually publish their artifacts (or jar files) into a central repository.
The solution is to use both a central (for common libraries) and local (for your project) repositories. You can take a look at my public projects and especially the ivysettings.xml file because they use exactly this very principle.