there should be two classes called "Library in your workspace:
org.eclipse.swt.internal.Library in \org.eclipse.swt\ws\win32\swt.jar org.eclipse.core.internal.plugins.Library in \org.eclipse.core.runtime\runtime.jar
Because you have compile errors in SWT I assume you tried to import SWT as source. Do you need this as source? If not, you could simple import the JAR and attach the source.
If the above information does not help, you should post what this ("with a couple of variations." ) means, together with the files that have the compile errors and the Java Build paths for your projects.