If you have win98 first edition it does not have ICS(Internet Connection Sharing)if it is 98se then you will be able to share your BB connection.
You need a 10/100 network card for each machine connected together with a length of crossover cable. You set up the network in XP by going to start/programs/accessories/communications/network setup wizard. Follow the instructions.
Then put your XP disk into the 98 machine and when it opens choose perform additional tasks/setup home or small office network.
Follow the instructions this will setup the network on the 98 machine.
If you do not have an XP disk when you set up the network on XP it will give you the opyion to make a floppy, do this and use it to set up the network on the 98 machine