You might want to get multi-channel USB external sound card as well. I have the Creative Audigy NX USB and I can wire that up right to a mixer and use the laptop as if it were two turntables. It's as close as you can get to mixing on actual turntables but by using a laptop. I used Traktor for this and it works great. The only problem I had was latency -- no ASIO support on this particular soundcard, but there are others that support it.
