You dont say what flavour of broadband but it will be just a matter of setting up a small network (if you have XP on one of the machines this is very simple) connect the modem to one machine and configure the internet connection sharing facility. as i say if you have XP the network connection wizard takes care of all of for you .
If you have'nt got on board built in network cards then the answer is yes, just bog standard 10/100 pci cards will do. Rather then buying a hub, buya switch, a small desktop type with 4 or 5 ports wil do and there is hardly any difference in price between hubs and switches thse days but switches are more efficient.once you have installed your hardware follw on with the advice from horiz5. One thing to bear in mind, i Believe when using XP with "ICS" you will need to disable the built in firewall and buy a third product like Norton's Personal firewall. Not 100% about the firewall but I sure somebody will read this an advise. Good Luck!