I have been asked to dj a halloween party. Will a multi disc changer work or do I need two separate players?

If you want to mix the music then you'd be best off with two pioneer cd dj systems along with a mixer (and get used to them prior to the event). If you don't have that I'd suggest trying to do some mixes at home on a pc to play or just wing it. Nothing more anoying than two songs that arn't beat matched (this is known as a train wreck in the DJ world... and they suck). With what you have you could do it as long as the multi changer doesn't mess you up! Set it up now and try it out if you can.