After successfullky importing from a few sources, I went back to try one more. This time, however, I couldn't get the JDBC Importer to work. Here's the sad tale:

Choose File > Import
Select the JDBC metadata importer
Click Next
<wait a long time>
Get next screen, but sources combo box and Next button are disabled.

Somewhere along the way I get an exception like:
Error 2009-04-21 14:59:08.708 Unhandled event loop exception
java.lang.IllegalArgumentException: Argument cannot be null
at org.eclipse.swt.SWT.error(SWT.java:3761)
at org.eclipse.swt.SWT.error(SWT.java:3695)
at org.eclipse.swt.SWT.error(SWT.java:3666)
at org.eclipse.swt.widgets.Widget.error(Widget.java:446)
at org.eclipse.swt.widgets.Combo.add(Combo.java:163)
at com.metamatrix.ui.internal.util.WidgetUtil.setComboItems(WidgetUtil.java:917)
at com.metamatrix.ui.internal.util.WidgetUtil.setComboItems(WidgetUtil.java:895)
at com.metamatrix.ui.internal.util.WidgetFactory.createCombo(WidgetFactory.java:441)
at com.metamatrix.ui.internal.util.WidgetFactory.createCombo(WidgetFactory.java:411)
at com.metamatrix.modeler.internal.jdbc.ui.wizards.JdbcSourceSelectionPage.createControl(JdbcSourceSelectionPage.java:184)
at com.metamatrix.ui.internal.wizard.AbstractWizard.createPageControls(AbstractWizard.java:109)
at com.metamatrix.ui.internal.wizard.AbstractWizard.createPageControls(AbstractWizard.java:97)
at com.metamatrix.modeler.internal.jdbc.ui.wizards.JdbcImportWizard.createPageControls(JdbcImportWizard.java:219)
at org.eclipse.jface.wizard.WizardDialog.createPageControls(WizardDialog.java:669)
at org.eclipse.jface.wizard.WizardDialog.setWizard(WizardDialog.java:1083)
at org.eclipse.jface.wizard.WizardDialog.updateForPage(WizardDialog.java:1142)
at org.eclipse.jface.wizard.WizardDialog.access$2(WizardDialog.java:1139)
at org.eclipse.jface.wizard.WizardDialog$4.run(WizardDialog.java:1128)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.jface.wizard.WizardDialog.showPage(WizardDialog.java:1126)
at org.eclipse.jface.wizard.WizardDialog.nextPressed(WizardDialog.java:820)
at org.eclipse.jface.wizard.WizardDialog.buttonPressed(WizardDialog.java:369)
at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:624)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1158)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3401)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3033)
at org.eclipse.jface.window.Window.runEventLoop(Window.java:825)
at org.eclipse.jface.window.Window.open(Window.java:801)
at org.eclipse.ui.internal.handlers.WizardHandler$Import.executeHandler(WizardHandler.java:146)
at org.eclipse.ui.internal.handlers.WizardHandler.execute(WizardHandler.java:273)
at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:281)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:476)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
at org.eclipse.ui.internal.handlers.HandlerService.executeCommand(HandlerService.java:169)
at org.eclipse.ui.internal.handlers.SlaveHandlerService.executeCommand(SlaveHandlerService.java:247)
at org.eclipse.ui.internal.actions.CommandAction.runWithEvent(CommandAction.java:157)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:583)
at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:500)
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:1158)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3401)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3033)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2382)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2346)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2198)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:493)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:288)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:488)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:193)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:386)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:549)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:504)
at org.eclipse.equinox.launcher.Main.run(Main.java:1236)

Whole log and screenshot are attached.