java.lang.NoClassDefFoundError: org/eclipse/core/runtime/IProgressMonitor

For some reason my eclipse can't find the IProgressMonitor interface. I've added the following jar files from the plugin file to my classpath:

org.eclipse.core.runtime_3.4.0.v20080512.jar
org.eclipse.jface_3.4.0.I20080606-1300.jar
org.eclipse.swt_3.4.0.v3448f.jar
org.eclipse.swt.win32.win32.x86)3.4.0.v3448f.jar
org.eclipse.ui.workbench_3.4.0.I20080606-1300.jar

Based on the class's package, I'd think that it belongs in the org.eclipse.core.runtime jar, but when I look in that jar file, I can't find the IProgressMonitor class. Does anyone know what jar files I should be using to use JFace/SWT? Am I using the right files?