Virtual Turntables is a program for Windows what allows real-time
MP3 mixing. When you load an MP3 song in the program, an interface similar to a
DJ cd deck appears on screen. Each loaded MP3 gets one of these.
The interface gives you the ability to change the pitch/tempo of the song. It's got "nudge" buttons to move the song position ahead/back a little.
Virtual Turntables also includes a virtual mixer with a level control for the virtual MP3 decks and a crossfader. It can use the left channel of your sound card for headphones (to cue an MP3) and the right channel for the output to your amplifier. It can also use multiple sound cards, if you have them.
Virtual Turntables is a shareware application from Carrot Innovations which costs $37, and is available at carrotinnovations.com.