How Do I Select a Checkbox on Update

[adenwalker]

I know I've posted quite a bit today but i am making some big modifications to a big database.

Basically, when a record is updated (information in the record is changed) a checkbox (Update) is automatically selected. How can i do this.

Also i want to be able to click a button that will clear the checkboxes which are selected. How do i do this?

Thanks very much
Aden