As Finagle pointed out, the comet at it’s closest approach would be .5 AU from the Earth. That’s some 43 million miles (give or take a million or two), and the most likely thing that would happen if the comet did explode is that it would burst in a manner similar to the Death Star (minus the ring shockwave from the SE version), so you’d have hunks of it flying off in all directions. Most of them would probably stay in the same general area for quite some time (the impactor’s traveling at roughly 23K mi/sec.), so we’d definately miss any debris on this pass. What we would get (if anything) on the next pass depends entirely upon how long it takes the comet to complete an orbit and what (if any) celestial bodies are nearby as it makes it’s loop. If the hunks pass too close to Jupiter, they’ll no doubt get sucked in. IAC, we’ll have ample warning to prepare in the incredibly remote event that something large enough to be a concern starts heading this way.
Sam Stone, it’s supposed to get bright enough to be seen with the naked eye when it hits because the amount of material kicked up. Of course, predictions of how bright a comet’s supposed to be are notoriously off. Halley’s comet was pretty dim, IIRC, and so was one that appeared in the 1970s. I was more impressed by the comet which passed through the solar system the year before Hale-Bopp showed up than I was by Hale-Bopp.