I am an avid watcher of the Science Channel, and love doing casual research into all kinds of science (mostly computer and space-centric topics) and have come to the conclusion that Mars will not be terraformed for centuries, more likely millenia. Of course, I'm hardly qualified to make such a decision, so I've come here for all of your opinions. Not that you'll change my mind, just that it'd be an interesting discussion

There are no less than four (maybe five) attributes that any world must have to be brought to an Earth-like state.

1. An Earth-like Atmosphere: This is of course the most obvious of them all. Without a proper atmosphere a colony is restricted to heavily shielded installations to protect from the harsh environment, be that the existing atmosphere, the lack there-of, or cosmic radiation that is not being stopped by the (non)atmosphere.

We can cultivate an atmosphere through various means, but they almost all depend on existing sources of water. Which is yet another requirement that we can't count on even on Mars, even though Scientists are farely certain there is water somewhere under the surface.

2. A Strong Magnetic Field/Iron/Nickel Core: The planet in question must have an Iron and Nickel Core in order to maintain a powerfull magnetic field, or energetic particles emitted by the sun will burn away the atmosphere that we so lovingly cultivated. This magnetic field also influences our weather, somehow, by-proxy, I think... If this can be verified/debunked that would be great. At any rate, that magnetic field is essential to protect the new atmosphere.

3. The planet must be Near 1G: Meaning that it must have a level of surface gravity very near that of Earth. To much and our bodies cannot handle it, to little and we start to fall appart, not to mention that the atmosphere will slowly leak away.

4. Lastly, it must have A Satellite: By that I mean a Moon. The Moon does a wealth of good to the Earth. It stabilizes Earth's orbit, giving us predictable seasons and stable weather (compared to the rest of our star system). It also creates the tides, which are important to alot of Earth based life forms. Not to mention the huge number of impacts the Moon takes for us. I think there is more, but the stability of the planet's rotation is so important that nothing else matters.

I also believe that active plate tectonics are essential, but I don't remember why I came up with that, so I didn't include it in my list.

Here are the ways these problems can be addressed, granted most of these solutions will not use current technology, because current technology will not suffice.

1. Atmosphere: Assuming there is frozen water, you introduce large amounts of carbon dioxide into the atmosphere to increase the planet-wide temperature enough to melt the ice. This would release more CO2 and continue to warm the planet, as well as introduce water vapor into the new atmosphere. After a certain point algae is introduced (most likely geneticaly engineered for the task) to increase nitrogen levels. When nitrogen levels are high enough, and enough water is available, higher level plants (more evolved) are introduced to increase oxygen levels. In the case of Mars there are huge levels of Oxygen tied up in Iron Oxide all over the planet (that is why Mars is a rusty red color) which can be released when a great deal of energy is applied. In this method you could create an Earth-like atmosphere in a few centuries, if we started next week   

2. Magnetic Field/Iron Core: This one is simple, tractor beam (or attach a rocket to) a big hunk of iron, or lots of pieces of iron, and smash it into the planet. If your lucky the impact will melt a large portion of the surface and cause the heavier-than-rock iron to sink to the core of the planet, thus supplanting the normally rock core with an iron one. The impact will have to be sufficiently large to melt enough of the rock to get all the way to the bottom or the magnetic field will be off-center at best, and not work at the worst. You also don't want to blast the whole planet apart, unless your trying to make a moon Obviously this step will have to be done before the formation of the atmosphere.

3. Earth-like Gravity: Basically this will be done in the same step as the construction of the iron core. By introducing heavier elements at various levels, or by sending other other large mass objects (perhaps from the asteroid belt) to the planet a higher level of gravity could be achieved.

4. Natural Satellite(Moon): Either piece one together from asteroids and meteors to achieve the right size at the right distance or do it the way the Earth got its moon. The first method is more likely to happen soon... well sooner.

By gathering together many large objects, again from the asteroid belt, you could eventually form a moon. At first you may need to maintain their relative position to eachother and the planet. Eventually their mutual gravity would draw them together, and after a great deal of time the increasing gravity of the object would cause it to become more cohesive, eventually becomeing a sphere. This process could be sped up if the initial objects are of a super heavy element, such as Uranium, but an inert element/substance would probably be a better choice.

The second would be to replicate the birth of our own moon. It is theorized that a large object, roughly the size of Mars, struck the early still-molten Earth. This impact threw off huge amounts of material into orbit. This material eventually coalesced into our moon. This method would make creating the Iron Core easier because it would most certainly melt the entire planet, allowing the iron to sink all the way to the bottom. However, it is extremely risky, because there is no way to be sure it will turn out properly. If to much is ejected than the mass of the planet may become to small, if to little than you just wasted your time and energy, and it takes alot of energy to move a planetoid! You also don't know if it will land in the right orbit (the correct distance). It gets even more complicated when you factor in that you need the distance to be just right for the ratio between planetary gravity and lunar gravity. This method is just too unpredictable.

Both methods could take centuries to create a moon.

As to my (almost) certainty that there must be active plate tectonics, well you'd introduce radioactive elements to the iron/nickel core when you insterted it, such as Uranium, Thorium, and Potassium. These elements exist at the center of the Earth, within the Iron/Nickel core, and create a kind of atomic engine that keeps the interior of the Earth very hot. Without it the Earth would have cooled after less than 100 million years after the formation of the moon, this would have eliminated plate tectonics, and thus made life impossible, for some reason I can't remember.

Okay, that is my rediculusly long post. Thoughts?