Sharing the internet connection with a Windows 98 PC is no different from any other operating system.
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.
To enable “Internet Connection Sharing” in Windows XP, open the Network Connections folder, right click the actual internet connection (modem connection), select Properties and then the Advanced tab. Tick the box “Allow other network users to connect through this computer’s Internet connection”.
When you enable "Internet Connection Sharing" on the Internet connection, it automatically configures the network adapter used for your "private network connection" with the IP address 192.168.0.1 and subnet mask 255.255.255.0. If you have more than one adapter available for this purpose, e.g. both a "Local Area Connection" and a "Wireless Network Connection", you will have a drop down list from which to select the appropriate adapter. The TCP/IP settings for the "Client" PC's network adapter (your Windows 98 PC) should be set to get the IP address automatically, which it does by DHCP from the "Host" PC. Also, 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.
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, these need to be configured to allow access to the networked computers. This may involve adding their IP addresses in a "trusted" area.