Try executing this SQL statement:
SELECT name FROM sysobjects
WHERE type = 'U'
In SQL Server 2000 (and probably 7 -- I haven't checked), this will return a resultset of a field of type SYSNAME which is functionally identical to NVARCHAR(128). In SQL 6.5 it returns a VARCHAR(30).
In sysobjects, "U" in the type or xtype field indicates a user table.
Just remember -- you should NEVER update or delete sysobjects directly! (Or any of the other system tables.)
You can get the names of all the other objects in the database by querying sysobjects, if you know the type field values. Look up "sysobjects" in SQL Server Books Online for more info.