particleman - 2:56 am on Feb 3, 2009 (gmt 0)
This registration business has come up before. I have done several custom carts and have setted on presenting the login screen and next to that a 3 line create account form with username and password after pressing the checkout button. This has worked pretty well as far as I can tell since the user doesn't need to enter a huge amount of information. When the checkout process is complete the information is populated to the customer info table.