Could it be possible for a planet in our solar system collide into another planet?

No. at least not within then many millions of years. All the planets are in stable orbits, and it would take a huge gravitational disruption to cause one planet to deviate so as to hit another. Much more likely is that a planet gets hit by a comet or asteroid. These sorts of collisions are relatively common - see for example the crash of Comet Schumaker-Levy 9 into Jupiter back in 1994: Comet Shoemaker-Levy 9 (NSSDC) (http://nssdc.gsfc.nasa.gov/planetary/comet.html)

could it be possible that a asteroid as big as, let's say Mars, flew past a planet and disrupt another? Is it possible that there is a asteroid as big or almost as big as Mars? What would happen if one collide to a planet like Earth? Watch would happened to us?

could it be possible that a asteroid as big as, let's say Mars...
Asteroids are never as big as planet Mars. Not even as big as dwarf planet Pluto.

The only direct cause of disrupting the orbit of planets around the sun is the passage of another solar system near to sol. This can happen when the solar system is travellling through the thick arm of the galaxy.

Another cause for possible disruption occures when the solar system is dipping up or down the galaxy disc. That happens about every 64 million years. Asteroids from the outer circle of the solar system are affected and send on their way to the inner circle. On their way they can (near) collide with planets, and affect their orbits if the asteroids are big enough and get near enough to one of the smaller planets.