VSS plugin in eclipse - plugins

Question

What happens when a plugin is added into an eclipse ?
What all the registries eclipse does internally ?
We have a product which is similar to that of eclipse .We are trying to add version control onto that . CVS and SVN jars were added into the plugin folders and projects added into workbench is showing SVN and CVS options . But when it comes to VSS, apart from jar file it is expecting VSSplugins folder but after adding VSSplugin folder it was showing VSS configuration option .After adding location details and saving and when we look for Team tab it is not showing any option(Options like checkout,Checkin.. etc).
And the workspace log is showing exception as
java.lang.NullPointerException
at org.vssplugin.ui.LabelDecorator.<clinit>(LabelDecorator.java:72)
at org.vssplugin.core.VSSPluginProvider.addProject(VSSPluginProvider.java:1457)
at org.vssplugin.ui.ConfigurationWizard$1.exec(ConfigurationWizard.java:86)
at org.vssplugin.core.SyncNotificationOperation.execute(SyncNotificationOperation.java:85)
at org.vssplugin.core.WorkspaceSyncModifyOperation$1.run(WorkspaceSyncModifyOperation.java:71)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1800)
at org.vssplugin.core.WorkspaceSyncModifyOperation.run(WorkspaceSyncModifyOperation.java:85)
at org.vssplugin.ui.UIUtils$2.run(UIUtils.java:233)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.vssplugin.ui.UIUtils.run(UIUtils.java:230)
at org.vssplugin.ui.UIUtils.run(UIUtils.java:222)
at org.vssplugin.ui.ConfigurationWizard.performFinish(ConfigurationWizard.java:82)
at org.eclipse.jface.wizard.WizardDialog.finishPressed(WizardDialog.java:752)
at org.eclipse.jface.wizard.WizardDialog.buttonPressed(WizardDialog.java:373)
at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:624)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3910)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3503)
at org.eclipse.jface.window.Window.runEventLoop(Window.java:825)
at org.eclipse.jface.window.Window.open(Window.java:801)
at org.eclipse.team.internal.ui.wizards.ConfigureProjectWizard.openWizard(ConfigureProjectWizard.java:224)
at org.eclipse.team.internal.ui.wizards.ConfigureProjectWizard.shareProjects(ConfigureProjectWizard.java:124)
at org.eclipse.team.internal.ui.actions.ConfigureProjectAction$1.run(ConfigureProjectAction.java:39)
at org.eclipse.team.internal.ui.actions.TeamAction$3.run(TeamAction.java:265)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.team.internal.ui.actions.TeamAction.run(TeamAction.java:262)
at org.eclipse.team.internal.ui.actions.ConfigureProjectAction.execute(ConfigureProjectAction.java:33)
at org.eclipse.team.internal.ui.actions.TeamAction.run(TeamAction.java:514)
at org.eclipse.team.internal.ui.actions.TeamAction.runWithEvent(TeamAction.java:548)
at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:241)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:584)
at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:501)
at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:411)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3910)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3503)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)