Let me know and I can get more detailed.
Essentially,
1. Using SQL Management Studio, you can right click on the SQL install(instance) and create a new database. Call it Altiris1 or AltirisNew (or whatever, just so you can differentiate it.
NOTE: Do this BEFORE you change anything on the NS.
2. It will be a 'blank' or standard SQL database, and will take your default properties either your DBA or Microsoft has so kindly set for you (database and log location, memory usage, security, etc).
3. Make sure you login to the server via a 'session 0' terminal services (mstsc /admin or mstsc /console) or be on an otherwise direct connection to the server.
4. Open the web browser and do a 'mini-setup' by going to: http://localhost/Altiris/NS/Install/NSSetup.aspx. go through the 4 steps, confirming the details. When you get to the final step select the new database (instead of existing). This process will take some time, but will essentially create all the tables Altiris needs.
5. Nothing should need to change on the regional server(s) inventory forwarding rules. Whenever they next forward, the data will be populated on the reporting server.