Following up on my own post (immediately below this one; slow discussion at this point I guess ;~) I allowed the issue to stew overnight and here is the answer.
In my particular case, I am working against an Internet MS SQL database (which I cannot access via the Enterprise Manager or the Query Analyzer tools). It's hosted space and I can only access MY specific SQL database via a primative web interface....
In my research, I seem to have discovered that SQL Server includes a *default* stored procedure named "sp_adduser" which is used for adding database users and roles to the admin side of the database (not what we want here at all!). In any event, when the join.asp page calls the stored procedure in it's default configuration, it is actually calling the system level "sp_adduser" not the database level "sp_adduser" created in these scripts.
In my case (a personal SQL database hosted on a remote SQL Server installation), I had to edit the join.asp page as follows:
Set oCmd = GetStoredProcedure(oConn,"[databasename].sp_adduser")
In my case, by adding the name of my database to the stored procedure call, it now accesses the "correct" stored procedure.
I have tested this on my website and it now works. New users are now able to join the site.
Perhaps a different naming convention is called for in the example to avoid this kind of problem (or at least an explanation of the possible confusion)?
Thanks, (and I will now go about the process of testing out the scripts and db interaction to truly evaluate the example--it was kinda hard before...)