Hmm by old project, do you mean pre-version 3.x? If so, then in Cordova 2.x onwards, there was the addition of a 'create' script which would build a default project for you where you can edit it. But you had to download that script with each new version of Cordova.
As of Cordova 3.x, they started distributing Phonegap via npm using node.js. Which integrated deeper into the operating system but meant it was readily available more easily. As a result, you can do `phonegap create` wherever in your directory structure.
So to verify, can you confirm what happens when you do the following please:
- phonegap -v
- phonegap create Test
- cd Test
- phonegap plugin add org.apache.cordova.device
- phonegap platform add [ios|android|wp8]
- phonegap build
This should get a simple project up and running. You'll then need to import this into Eclipse (open Eclipse and go to File > Import existing code into workspace then navigate to your phonegap directory and look for platforms/[your-platform].
BTW if you're using Cordova and Phonegap (which is what I also do), then replace every Phonegap instance in my answer above, with Cordova (lower-case in the CLI).