If I'm driving car A at 60 mph, and you're driving car B at 60 mph, and you crash into me head on, then it could look to me as if you're approaching me at 120 mph before the crash. This is called a "Galilean" addition of velocities (they just add together).

If you try to do the same thing at close to the speed of light, since nothing can move faster than the speed of light, you get an extra factor in the equation, so you can't just add velocities, since, as you point out, that would lead to velocities faster than the speed of light. The actual equation to correctly add really fast velocities together is here:

http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_Theory_of_RelativityOf course, if you're going slow enough, then the extra factor that appears because of special relativity is negligible, and you can just add velocities together.

Finally, to answer your question, if two rockets slammed into each other, and each had a speedometer that said "0.6 times the speed of light," rocket pilot A would say that rocket B is coming at him at a speed of around 0.88 times the speed of light.