You need to have a computer interface with as many individual channels as your recording needs require. This interface should be either firewire based or PCI slot based. USB is not adequate for multitrack recording. There are lots of options available. A selection of quality interfaces can be found from RME, TC Electronic, Presonus, Yamah, Mackie, Allen & Heath. Which one is correct for your needs will depend on what those needs are and what kind of work flow is most efficient for you personally.