The Art of Aerobraking
At school we're actually designing a Mars Sample return Mission. As a result I've been researching many different methods for orbital insertion. AeroBraking is an excellent method to change your orbit. As an Example the Magellan spacecraft was orbiting venus and wished to enter a more circular orbit. It was calculated that 900 kg of fuel would be needed to do this traditionally, more than the spacecraft had. Using aerobraking only 38 kg of fuel were used. Of course the downside is the manuver took 3 months to perform.
For atmospheric entry however parachutes alone are not enough. Mars's atmosphere is 1000 times less dense than Earths. What parachutes are used for is to give a huge reduction in speed, from about 900 MP to about 160 MPH. A parachute that does this weighs about 10 KG. A parachute that would bring pathfinder to a survivable landing would have a 250 ft diameter and weigh 420 kg, more than the lander itself! It's much better to slow down some with a parachute then use retro rockets in one form or another.