Work-in-progress for the OSCommerce enrolment plugin. See http://moodle.org/mod/forum/discuss.php?d=60259
So far, I'm using the Catalyst specific OSCommerce branch, which has some modifications to suit the enrolment plugin for Moodle. Most of the modifications either streamline the purchase process, or disable areas of OSCommerce which are not used in this set-up.
The enrolment plugin has been upgraded to suit Moodle 1.7, but needs some checking to see if anything has been missed in the changes from Moodle 1.5 (custom branch, however; closer to 1.6) to 1.7.