I would try something like this.
@browser.div(:class => "forum-group").label(:class => "selectable").check
However, I am not sure you can do a ".check" on a label element. You could also try
@browser.div(:class => "forum-group").checkbox(:id => "chkNoEmail").check
Or, since I dont think it is an actual check box, you could try ".click" instead of ".check" on either one of them, I still do not think you can do either action on a label element though.