See http://groovy.codehaus.org/Emacs+Groovy+Mode.
Be sure to also read informations inside inf-groovy.el. Here is environment juggling that I use in order to make it work.
;environment (defvar utils-dir "/home/sagasu/utils") (setenv "JAVA_HOME" (concat utils-dir "/java/jdk1.6.0_26")) (setenv "GROOVY_HOME" (concat utils-dir "/groovy/groovy-1.8.0")) (setenv "MAVEN_HOME" (concat utils-dir "/worek/maven/maven-2.2.1")) (setenv "PATH" (concat (getenv "PATH") ":" (getenv "JAVA_HOME") "/bin" ":" (getenv "GROOVY_HOME") "/bin" ":" (getenv "MAVEN_HOME") "/bin"))