Alrighty. I have an iPad (one) and decided to update the software. The software would, for some fantastic reason, cease downloading about .1mg before it had completed - rendering my iPad useless (as the screen was locked on the 'connect iPad to to iTunes via USB" message). I tried reloading the software from two other computers (PC and laptop - all Windows), still nothing.
Before calling Apple (or throwing the thing at a wall), I decided to try it one more time on my own computer using a USB port that I hadn't used before (ever..). And, by God, it actually worked. Shat a brick.
TL;DR: try using a different USB port.
Hope this helps ^_^