The Eclipse 3.3 - 3.6 launchers for Windows have a problem with the Oracle/Sun Java VM version '1.6.0_21'. You have two choices to work around this:

1. switch back to '1.6.0_20'
2. add the following line after "-vmargs" to your eclipse.ini:
-XX:MaxPermSize=256m

See https://bugs.eclipse.org/bugs/show_bug.cgi?id=319514 for more details.