Change usercheckout.php sequence possible?

Is it possible to change the sequence of steps within the usercheckout.php process - specifically to put the login / registration step towards the end rather than at the start? From a usability point of view, hitting new users with a registration screen at the first step can be a traffic killer. Many classifieds sites allow visitors specify a username and password towards the end of the ad posting process for this reason so I am wondering if this approach can be achieved by modifying usercheckout.php?

[Lhotch +]

It can be modified if you have the developer version but will require decent knowledge of PHP scripting.

[seymourjames +]

An issue i can see with this approach is those placing multiple adverts. You will need to manage those types of customers. They will not wish to enter registration info more than once.