It is not possible to run NetBenas 5.5. with platform of NetBeans 6.0:

Warning - could not install some modules:
   Platform - The module named org.netbeans.modules.options.api/1 was needed and not found.
   Welcome Screen - The module named org.netbeans.modules.autoupdate/1 was needed and not found.
   NetBeans Module Projects - None of the modules providing the capability org.netbeans.api.javahelp.Help could be
installed.
   Java Project Support - None of the modules providing the capability org.netbeans.modules.project.uiapi.ActionsFactory
could be installed.
   User Utilities - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   Keymap Options - The module named org.netbeans.modules.options.api/1 was needed and not found.
   XML Core - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   HTTP Monitor - None of the modules providing the capability org.openide.util.HttpServer$Impl could be installed.
   Core - UI - The module named org.netbeans.modules.options.api/1 was needed and not found.
   JSP Parser - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   JPDA Debugger UI - None of the modules providing the capability org.netbeans.api.debugger.jpda.JPDADebuggerEngineImpl
could be installed.
   JPDA Debugger UI - None of the modules providing the capability org.netbeans.spi.debugger.ui could be installed.
   CSS Support - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   Database Core - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   Java Language Model Implementation - None of the modules providing the capability org.netbeans.api.mdr.MDRManager
could be installed.
   Form Editor - The module named org.netbeans.modules.options.api/1 was needed and not found.
   JPDA Debugger Ant Task - None of the modules providing the capability org.netbeans.modules.debugger.jpda.ui could be
installed.
   Auto Update UI - The module named org.netbeans.modules.options.api/1 was needed and not found.
   Ant - None of the modules providing the capability org.openide.execution.ExecutionEngine could be installed.
   Ant - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   Ant - The module named org.netbeans.modules.options.api/1 was needed and not found.
   Database Explorer - None of the modules providing the capability org.netbeans.api.javahelp.Help could be installed.
   Database Explorer - None of the modules providing the capability org.openide.windows.IOProvider could be installed.
   Task List Core Support - None of the modules providing the capability org.netbeans.api.javahelp.Help could be installed.
   XSL Support - None of the modules providing the capability org.openide.util.HttpServer$Impl could be installed.
   Options Module - Editor - The module named org.netbeans.modules.autoupdate/1 was needed and not found.
   Options Module - Editor - The module named org.netbeans.modules.options.api/1 was needed and not found.
   157 further modules could not be installed due to the above problems.