The bulk of my contribution is just an explanation of how to make the template changes. The actual code to allow optional password was from PaulM. And then after playing around, I figured out how to allow duplicate emails. I don't even feel right calling it "my" contribution. I feel more like I just gathered information for you and zipped it up.

To make it work, you really only need to edit 3 files, and they are very small edits. Everything else was just changes to the templates, like removing the login fields, password fields, etc. Not a really big deal, but better done on a sample cart first so you can get the idea of whats going on. When it comes down to it, if you are capable of editing tpl files and you understand what you are doing when you make those edits, its really quite simple. And I'm always here to help.