networking win2k,winxpPro,winxpHome

Trying to network 3 machines. Computer 1 Win xpPro. Computer 2 Win2k. Conputer 3 WinxpHome.
They are wired together to a netgear switch and that is connected to a cable modem. All machines can access the internet. Computer 2 can see all machines and access shared files on computer 3. Computer 3 can see computer 1 and access shared files. Computer 2 can see workgroup but is denied access to computers 1 & 3. All computers have the same workgroup and all are set to automatic for Tcpip. Do I need to add an account/user on each machine for each other machine? File sharing is enabled on all machines. Do I have to keep the logon screen or can I have it set to automatic logon?