SQL Server Licensing (what Version Should I Use?)

Hello,

I am very confused about the licensing of SQL Server 2000 and 2005 (various editions),
and any light you can shed will be greatly appreciated.  I am learning VS2005, and
need to build a website.

1.  I know what a Client Access License (CAL) is.

2.  I know what a processor license is.


My ASP.NET website might have 10 users, 100, or maybe 1,000 (I don't know at this point).
They will have anonymous access to a main page from which they will have to log in,
and from that point on be using SSL for anything they do.

I am getting conflicting information regarding licensing.

Questions:

1.  Can SQL Server 2005 Express support what I need to do?  (possibly many users)

2.  Other than some of the fancy replication, analysis, etc that Express does not
    have, is there a good reason not to use Express Edtion?

3.  Regarding SQL Server 2000 or 2005 (NOT Express): 
    Does a single web application act as a single user thus the
    web application requires only one CAL. 
   
    In other words:  I am the only person who has direct access to the database.
    The ASP.NET web application will also have access to parts of the database.
    Will this scenario count as 2 "CALs"?