It is possible to add logic to InfoPath forms so that certain fields are displayed based on the value of another field. For example - if a user fills in their age on a form as being 17 or greater then the question - Do you hold a full driving license? - becomes visible. In the UK this question is not relevant if the user is less than 17.
To do this using InfoPath 2007 you will need to create a form with the two questions - How old are you? and - Do you hold a current driving license? Add a two row, two column table to your form. Add the How old are you? question in the top left box. In the top right box add a text box that takes a whole number, call it Age and set it with a default of 0.
Next, merge the two cells in the bottom row and add an optional section control. Insert a table with one row and two columns to the optional control. Add the Do you hold a current driving license? question to the table. In the right hand table cell add a drop down list box that has options of select..., Yes and No.
Set the section properties to display the section by default. You should now have something that looks like this when previewed:
Next right click on the optional section and select 'Section properties...' Select 'Display' and then 'Conditional Formatting...'
Click Add - set the condition to be Age is less than or equal to 16 and check the 'Hide this control' option.
Preview the form again and you should see:
Enter an age greater than 17 to display the optional question:
Change the age to less than 17 and the question will be hidden again.