screen-scraper allows for Java libraries to be added to the classpath. Simply copy any jar files you'd like to reference into the lib\ext folder found in screen-scraper's directory. The next time you start up screen-scraper it will automatically add the jar files to its classpath. Note that you'll still need to use the import statement within your scripts to refer to specific classes:
screen-scraper was built on a Java 1.5 platform. Your Java scripts must accept at least a version 1.5 JRE in order to compile and run properly.