I want to buy a dell inspiron 531 computer from costco. It has a TV tuner and a 56K PCI Data/Fax Modem. I know the TV tuner uses one of the two available pci slots, but does a data/fax modem use anothwer pci slot? I want to have an open pci slot so I can add a firewire port. If the data/fax uses a pci slot can I remove and replace with a firewire pci?

You can buy a PCI extension card that adds the amount of PCI slots available to your PC

If your on broadband internet (i.e. cable or Bell), then you can remove the data/fax modem card, unless you actually use your PC as a fax machine... :)