Because the version 7.0 of Tomcat is not supported directly by myeclipse 6.6，so you need to change something before using it .let's beginning ...
1.Windows-----preference ---myeclipse enterprise workbench ---servers ----Tomcat----Tomcat 6.x
fill the path of Tomcat at the blank zone .(like the picture )
2.add the JRE path at this place ,and name it
3.add Tomcat -Juli.jar path at this place ,and apply