Eventually, I figured out that I was thinking about it wrong.  There’s no such thing.  But there is such a thing as a custom box, and boxes can be made into tabs.  Furthermore, almost any tab can be made the default tab.  So here are the steps to create your own Welcome tab and make it the first thing people see:

• Add Static FBML to your Facebook page  (That’s what lets you create a custom box)
• - From your page, click “Edit Page”
• - Under “More Applications” at the bottom, click “Browse More”
• - In the “Search Apps” box, type “Static FBML”
• - Click on the “Static FBML” app
• - On the left, click “Add to my Page”
• Create a box named “Welcome” and design it however you want using FBML (similar enough to HTML)
• - Go back into “Edit Page”
• - Find “Static FBML” and click “Edit”
• - Change the Box Title to “Welcome”
• - Add your FBML code
• - Click “Save Changes”
• Change the box to a tab
• - Again, from the “Edit Page” screen
• - Find your “Welcome” FBML app
• - Click on “Application Settings”
• - Next to “Box” click “remove”
• - Next to “Tab” click “add”
• - Click “Okay”
• Make the new tab your default for your page
• - This time, from the “View Page” screen (looking at your Fan Page)
• - Click “Options” on the right
• - Click “Settings”
• - Change the “Default Landing Tab” to your new Welcome tab

Walt