You could make a custom field on the customer level that is required. That should do the trick. It is located under Global Settings -> Custom Fields. You'd want the type to be a checkbox, the value to be boolean, and the Label to be "I accept the terms and conditions" (Or some variation of that).
Pier Posthumus
AutoMagic Studios | Ecommerce Design and Development
Pier@automagic-studios.com
http://www.automagic-studios.com201-546-7577