I wanted to know about MEM(masters in engg management).i heard we need to give GRE for it .But I'm currently studying for CAT.HOW TO STUDY ?

I'm a third year computer engineering student. I want to do MBA after this but I still don't want to leave the technical aspect. what is difference in preparation for CAT and GRE (for MEM(masters in engineering management).I wanted to study for both. I'm currently preparing for CAT.Can i do both?