You can use a multi track program and have them cross fade into each other. Basically try to match the beats and then have one song fade out while the other fade in. All you would need is a program that supports multi track layering. Protools you can even tap out the beat for each track and then it will just drag right into the correct beat. unless you tap like a monkey drummer The best way would be to have two turn tables with high mid and low cutoffs. that way you could actually mix it up real nice like even giving hints by dropping a break or two from the next track mid song. Do you have access to some cd turntables?