We've all been keeping tabs on the rendezvous of the Deep Impact space craft with Comet Tempel 1 (that video link Tom provided is spectacular).
For curiosity's sake, here is the inner solar system at the time of the encounter, with the comet barely inside the orbit of Mars. The comet's five-and-a half year orbit keeps it inside the orbit of Jupiter. It reached perihelion (closest to Sun) the day after impact. The orbit is inclined by about 10 degrees to the plane of the solar system, and the comet was plunging through the plane just as the encounter took place. It will now follow Mars on around the Sun, but drifting out towards Jupiter.
Folks who worried that we might nudge the comet from its orbit and cause a collision with Earth need not be concerned. It's future colonists on Mars who must keep an eye on Tempel 1, and Jupiter is more likely to perturb its orbit than anything we throw at it.