Secure Pages

No e-Commerce site should be without SSL to provide secure transmission of sensitive data. With Drupal Secure Pages, SSL enabled server customers can have a secure shopping experience. Download & copy the module to your Drupal Installation's module directory, then activate the module at admin/build/modules.

Configuration
Administer> Site configuration > Secure Pages
uri – admin/settings/securepages

Enable Secure Pages: select the enabled radio button,

If you want to revert back to non-ssl for pages not listed in [Make secure only the listed pages] then check; [x] - [Switch back to http pages when there are no matches]. If you are going to secure your entire site then you don't have to check this.

Next choose either to secure every page or only listed pages radio button.

Some pages are listed by default, you can add others by using the format: from your URL if you set clean url's (recommended). You can also use “*” wild card.

To secure the checkout process add cart/checkou* to the list.

More Information
These instruction were successfully used on Drupal5.7,Securepages 5x-1.6
Download: http://drupal.org/project/securepages

Pages to protect: forum thread