Hello
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Insert Conditional Formatting on the Sections to Show/Hide them based on the selection made in the listBox.
Double Click on the Section to open the Properties.
In the Display Select tab click on Conditional Formatting and insert Conditions.
Select the <listbox field> in the first drop down and <is not equal to> in the second dropdown and the insert the text in the third dropdown
and check Hide this Control.
Repeat the same steps for the second section too.
I hope this will help you.
Kalyan G Reddy
Infopath MVP 2007 and 2008