Start with a Title window and use this as the "Shell" for everything you want to have.(Help,disclaimer,etc) Each portion can be split out into a new mxml component. So, you will have:
Shell.mxml (root)
help.mxml
disclaimer.mxml
welcome.mxml.
I would base each of the sub-components on a canvas to make the sizing and layout a bit easier.
The shell.mxml simply needs to have two main parts.
1. A link bar
2. View stack
The ViewStack will use each of your components that you have created. In order to do this you will need to make sure your title window(shell) imports the correct namespace. Change this accordingly.
xmlns:yourStuff="com.esri.solutions.flexviewer.widgets.yourStuff*"
<mx:LinkBar dataProvider="{ViewStack}"/>
<mx:ViewStack id="ViewStack" borderStyle="solid" width="100%" height="100%" color="0x323232" top="31">
<yourStuff:disclaimer id="disclaimer" label="Disclaimer"/>
<yourStuff:help id="help" label="Help"/>
<yourStuff:welcome id="help" label="Welcome"/>
</mx:ViewStack>
After you have the title window set up and your code for each component. You can use the PopUpManager to open the title window.
Unfortunately I don't have any complete code for you, but I hope this is enough to get you started. Please let me/the forum people know if you need any help.
Alex