I need to generate custom SIDs for users in my web application for use with Microsoft AzMan. What is the best way to do this? What do I need to know before doing this?

This is what I'm thinking, but I'm not sure if I'm missing something:

S-1-9-1234-{user_id + 1000}

S-{first revision}-{resource manager authority}-{domain (unique number for the specific app)}-{unique id for user}

UPDATE: Changed to resource manager authority because of David Crawford's blog entry: http://blogs.msdn.com/dc995/archive/2006/08/23/715021.aspx