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Actually you can. Using a custom tab control like this one (bottom of page) you can disable and enable certain tabs. When disabled you can't even enter the tab page.

You could use a custom tab control like this one (bottom of page) to disable the other tabs until there is text in the box. Edit: Also "An OnSelectedIndexChanging Method has been added to the TabControl so that you may cancel selection of a TabPage" until there is text