Terraforming Questions

I have been pondering terraforming.  I am of the understanding that a reason Earth can maintain an atmosphere and Mars can not is due to our strong magnetic field created by the convection of our molten core.  Mars lacks a strong magnetic field and thus is unshielded from the solar wind and it can not build up an atmosphere because it gets blown away.  Is this correct?  If so, is there a viable way to create a sufficient electromagnetic field as part of a terraforming project?<br /><br />-iggy