A basic microphone pre-amp with phantom power, and a audio interface of some sort whether it's PCI, USB or Firewire. You can get audio interfaces like the digidesign Mbox or Mbox 2 that are plugged into your PC via USB that also have a Mic pre amp with phantom power built in. This particular one I mentioned is only one of many out there to choose from in many different price brackets.

Have a look at sound on sound (pc music/music technology forums) . There is mountains of information available here