Hi Maria,
Changing the visibility of an object can be achieved with a bit of script. If you are using the latest version of LC Designer ES2, then there is a feature called Action Builder (under the Tools menu). This can build the script for you, by just specifying what actions you want based on conditions. You don't have to use Action Builder, it just may help.
The property you need is "presence". This can be set, using script, to visible, invisible, hidden, etc. You can also set the default presence at design time in the Object > Field palette.
One important thing to remember is that for this type of dynamic behaviour, you need to save your form as a Dynamic XML Form in the save-as dialog.
In earlier version of LC Designer you will need to script it yourself.
This example (http://assure.ly/h0zpOz) shows how you can script to change an object's presence property.
This example works up from a static table, up to dynamic tables (Tables 4 and 5) and subforms (Table 6), http://assure.ly/gBJYj9. Have a look at the buttons and the script in the click event.
Hope these help,
Niall
Assure Dynamics