Hi there,
Once you create the input form, locate the container that will be holding the input forms that you wish to make read only and add readOnly="true"
In the example below, I have created an input form with two content tabs (Customer and General) and I've made the input boxes read-only:
<createdBy _cs="Andrea Briceno"/>
<container codepage="1252" colcount="2" label="Campaign data" readOnly="true" type="notebook">
<container codepage="1252" colcount="2" label="Customer">
<input xpath="@firstName"/>
<input xpath="@middleName"/>
<input xpath="@lastName"/>
<input xpath="@emailAddress"/>
<input xpath="@countryCode"/>
<input xpath="@language"/>
</container>
<container codepage="1252" colcount="2" label="General">
<input xpath="@leadOrigin"/>
<input xpath="@brand"/>
<input xpath="@created"/>
</container>
</container>

Hope this helps
-Andrea