When emerging eclipse-sdk-3.2.1 under gentoo (or maybe also on other distributions), you may notice the following error message when trying to start it for the first time:
JVM terminated. Exit code=127 /usr/bin/java -jar /usr/lib/eclipse-3.2/startup.jar -os linux -ws gtk -arch x86 -launcher /usr/lib/eclipse-3.2/eclipse -name Eclipse -showsplash 600 -exitdata ff002d -vm /usr/bin/java -vmargs -jar /usr/lib/eclipse-3.2/startup.jar
/usr/lib/jvm/sun-jdk-1.6/bin/java: symbol lookup error: /home/danilo/.eclipse/org.eclipse.platform_3.2.0/configuration/org.eclipse.osgi/bundles/ 16/1/.cp/libswt-mozilla-gtk-3235.so: undefined symbol: _ZN4nsID5ParseEPKc
After some research in the internet, I finally found that the problem (in my case) was xulrunner. I couldn't just remove xulrunner though, as it is a dependency of mozilla-firefox. The solution was to remove xulrunner, and to rebuild the mozilla-firefox package with the xulrunner USE-flag turned off.
$ emerge --unmerge xulrunner $ echo 'www-client/mozilla-firefox -xulrunner' >> /etc/portage/package.use $ emerge -av mozilla-firefox
After that, you should be able to start Eclipse without the previous error messages.
Update: An even better solution to use eclipse is to unmask eclipse-3.3 in your package.keywords, and to use that version instead of 3.2... Apparently the above error is a bug in the eclipse-3.2-ebuild.