Your firewall settings allow "file and print sharing" and you can leave it on. My home "LAN" is a mix of XP Pro, Home and Win2K. All exist fine and share common printers. You need to make sure file and print sharing is turned on for all PCs, and you need to set up shares. Pro has some additional security features. If logon with a username/password is required on any local PC, a remote logon might be required unless the same users are all defined on all machines. There are some bumps and tricks but, to answer your question, they don't need to be the same OS and you can have the firewall turned on if the settings are done right.