How many cd drives do you have? it's possible to have each one use a separate volume control. As for fading, mp3's use the wave vol control and cd has their own, so you can do it that way. If you're gonna mix 2 mp3's, I'd just run 2 instances of your fav mp3 player. Same goes for the cd.
I've DJ'd before w/my mid-tower 300a@450 and 19" monitor. Monitor was a biotch to haul. Luckily I had a wireless mouse and keyboard so the actual playing of music was easier. 3 years ago was my first time and I had a pentium laptop. Mixed mp3's and cd's and it went ok. It was suggested to me that I use a cell phone as a modem and download requested songs. That'd work, but not sure if it's legal. I never did that cuz I stopped dj'ing w/my computer...just too bulky to move around and easily stolen.
BTW, how do you set the speed of the cd to match beats? MP3's are possible, but I haven't found a program to do it for cd's on computer.
Jay