I've had a similar requirement before and solved it by creating a Option Button with 2 buttons. The first one is for 'deselect all', then the other is for 'select all'.
I then set a rule on the first button with "if selected", there is an action of Checkbox1=false(), Checkbox2=false(), etc
On the other button, "if selected" rulse are Checkbox1=true(), etc
If neither is selected, the checkboxes stay untouched. There is no rule saying that either option button is default or required.
All is done right within IP2010 (and can be done in IP2007).