Do you have the JSP content type associated with the *.jsp file extension?
You can check this by going to Window > Preferences. In the navigation panel, expand General and select Content Types. In the Content Types panel, there should be a JSP type under the Text type. When you select JSP, do you see *.jsp listed?
p.s. Oh, and I'm using Eclipse on a Mac OS X (Snow Leopard), and the version of Eclipse is the Java (non EE) edition with Google App Engine Tools installed.