The short version of my issue at hand,
My problem was installing the Android SDK in Eclipse Helios on Windows 7 Enterprise 64bit, I was getting the following error:
Missing requirement: Android Development Tools 0.9.7.v201005071157-36220 (com.android.ide.eclipse.adt.feature.group 0.9.7.v201005071157-36220) requires 'org.eclipse.jdt.junit 0.0.0' but it could not be found
Having followed the advice above to ensure that the JDK was in my PATH variable (it wasn't), installation went smoothly. I guess the error was somewhat spurious (incidentally if you're looking for the JARs that correspond to that class, they were in my profile rather than the Eclipse installation directory)
So, check that PATH variable!