Sazza* thank you for your reply.
dez fowler+ I am running Norton Antivirus all the time and sometimes a software firewall Zone Alarm Pro. I have not yet downloaded the service pack 2 for XP's firewall.
AndySD^ Thank you for your suggestion I am using a Nat firewall that is built in with a Zoom X4 ADSL Modem and Networking 2 Pc's and a Mac via a hub. The instructions for the X4 state it is set by default it does not say I can configure the settings it just says as the first paragraph of Sazza's* reply. One thing I have done is on 'Bindings for local area connections' disabled the TCP/IP protocol and enabled it on the IPX/SPX protocol on both PC's that have XPHE as an OS on the Mac that is also on the network I have accepted Mac's standard settings. From all of your replies*^+ it would seem to me I must still run with a software firewall to protect out goings ( I am also on the Pc's running Lavasoft Ad-aware 6 plus) I was hoping the Nat firewall would be enough protection for the Pc's. with the changed settings on the protocol.Thus "Does a Nat Firewall require additional security".