Newsletter subscription option in checkout form.

I have installed the newsletter module.

http://drupal.org/project/newsletter

I have successfully add a field from the newsletter module with check box display in the customer profile in commerce. Now the user can check and apply to a news letter list while he is checking out. (Billing information).

I stuck now and can't figure out how to tell the newsletter the subscribers email to make the subscription complete.

Is here any one who did this and can help. Or is someone here who might to have a look at this.

Any suggestions very much appreciated.

Kirk