Music Players for DJs?

David Balazic asks "I'm looking for a program to play music (mostly mp3) at parties. What I want most is to be able to prelisten to next song(s) while the current one is still playing. I have a 4 channel sound card (sounblaster 64PCI) and I plan to hook up output 1 to an amplifier and output 2 to headphones. Is there a program for Windows or Linux that can use the four channels (for playing two independent stereo songs , not some "lame" 3D tricks)?"