Terraforming Mars by crashing comets into it

The idea was brought up by Marshall T. Savage and is part of his
Millenial Project ('colonizing the galaxy in 8 easy steps'). Basically
it's about evaporation of Mars's dry ice caps (they are made of carbon
dioxide) and thus raise the temperature. Send a comet (perhaps
multiple comets) crashing into Mars to bring in some water and to
liberate some carbon dioxide and water from the soil. Then use algae
to turn carbon dioxide into oxygen. The course of the comets would be
manipulated when they are very close to the Sun. Just give them a few
small "nudges". Given the resources and the money, could this really
work?

--
Matt Browne
My webpage is at http://www.meet-matt-browne.com
"As a race, we survive on planet Earth purely by geological consent."
Bill McGuire