To create a wired network for Internet access and File/Printer sharing, you have essentially two options:
1) Install a Network Adapter in each PC (if not already installed) and connect them directly with a "crossover" CAT5 ethernet cable. “Internet Connection Sharing” is then enabled on the actual Internet connection in the “host” PC and the “client” PC will have Internet access provided the “host” is running and online.
When you enable “Internet Connection Sharing” on the Internet connection in the “host” PC, it automatically configures the Local Area Connection with the IP address 192.168.0.1 and subnet mask 255.255.255.0. If you run the Zone Alarm firewall in your “host” PC, the Internet Zone Security level must be reduced from High to Medium or “ICS” traffic will be blocked. The “client” PC’s Local Area Connection should be set to get its IP address automatically, which it does by DHCP from the “host”.
2) The preferred option for connecting more than one computer is to use a broadband Router and, with ADSL, this should be a combined “Router/ADSL Modem”. All networked computers connect directly to the router with ‘straight-wired’ CAT5 ethernet cables.
With a router, it is the router which connects directly to the ISP and not one of the connected PCs. The router in turn allocates the IP addresses to the PCs, using one of the address ranges reserved for Local Area Networks, usually 192.168.xxx.xxx
Either of these options will additionally allow you to run File and/or Printer Sharing across the network.
If you are running software firewalls, the IP addresses of the networked PCs must be put into its "trusted" area to allow them to communicate with one another.
<<<ISP (Tiscali) informs me that I need to buy a wireless ASDL router and that "any would do".>>>
As above, you don't NEED to use a router, you can connect the two PCs directly and "share" the host's internet connection. The host PC, of course, needs to be online. Also, if you do buy a router, it doesn't need to be a "wireless" model, you can have a wired network.
<<<I assumed this would be a device in addition to the ASDL modem but having looked on the Internet to buy one I am now wondering if this is instead of the bundled ASDL modem>>>
ISPs supply USB ADSL modems because this is the cheapest option for them. A USB modem cannot be used with a router and so it is replaced by a combined "Router/ADSL Modem". If using a router, it is essential that you get one that is both a router and ADSL modem combined.
<<<If this device is connected to the computer which connected to the phone line what do I need for the other PC to connect>>>
Routers, whether "wired" or "wireless" models, normally have four LAN (Local Area Network) ethernet ports, so both PCs would connect directly to the router.