http://help.eclipse.org/help31/index.jsp?topic=/org.eclipse.jdt.doc.user/tasks/tasks-113.htm
Adding a JAR file to the build path
You can add a JAR file stored either in the workbench or anywhere in your file system to the build class path.
To add a JAR to your build class path follow these steps:
1. Select the project, and from its pop-up menu, select Properties. In the Properties dialog, select the Java Build Path page.
Click the Libraries tab.
You can now either add a JAR file which is contained in your workspace or which is somewhere else:
* to add a JAR file which is inside your workspace click the Add JARs button
* to add an external JAR file click the Add External JARs button
2. In the dialog that appears, select the JAR file that you want to add. Note that you can add multiple JARs at once.
Alternatively, to add an external JAR to your build class path follow these steps:
1. Select the project, and from its pop-up menu, select Build Path > Add external archives.
2. In the dialog that appears, select the JAR file that you want to add. Note that you can add multiple JARs at once.
