You need a MIDI interface or a soundcard with a built in MIDi interface. There are plenty of options around. Since you have firewire ports you can look at a firewire interface or PCI/PCIe.
E6600, Intel DQ965GF, 4 GB of RAM, Windows XP pro 32 bit RME FF800, LIQUID MIX, Cubase 4.1.3
