Alias with XP

Why is it necessary to create an alias in the Client Network Utility to be able to connect to SQL Server if you are running Windows XP?To clarify a little, it seems it is only necessary in XP. We don't have to create an alias when the client is running NT or 2000, only XP. Also, if the network connection goes down, we occasionally lose the alias and have to re-create it. Any ideas?sql