So does anyone use the FinalScratch Software?
http://www.zzounds.com/item--STAFINALSCRATCH
With this software, you can basically connect, two turntables (Mp3 or Vinyl, or both) and a turntable mixer, to your computer. I wanted to use this so that I could take vocals I was recording and scratch them. You can see what a setup would look like, if you click that link, and change the image (by clicking the Setup Example link, below the picture).