I'm going to assume that you're using Eclipse with the Robot Java Development plugin installed.
Is it that Eclipse isn't allowing you to import them, or is it just that Eclipse can't find them?
If it's the latter then make sure the WPILib JARs are in the build path. Right click on your project in the Project Explorer, then click
Properties... > Java Build Path > Libraries and see if the JAR files you need are there. It should look something like this:
http://i.imgur.com/GI5WzH9
The WPILib JAR files should have been automatically installed to your home directory in wpilib/current/lib when you installed the Eclipse plugin.