Minimum equipment needed is two NICs - any will do, a 10/100 card should be had for under a fiver - and a cross over cat 5 cable.
You will need to enable internet connection sharing - best done from XP and create a floppy from the wizard to run on the 98 machine.
Disadvantage is that you have to have the PC wiht the BB modem attached turned on to be able to access the net on the other PC.
Best way is to shell out for a router. Cat 5 cables between each piece of kit (not crossover this time). Set up is: Modem ---> Router ----> PC1 also Router ----> PC2
Disadvantage - dearer, Advantage - don't need both PCs on to access the net.