Problems with the current 4.2 build on the iPad have forced <a HREFApple to cancel a Wednesday release of the new OS and hold iOS 4.2 for the iPad and iPhone until next week. The expectation is that a new Gold Master is coming and that the final version will arrive in a few days.
You can try 4.2 right now if you want, however. I haven’t noticed a single issue with the current built and it makes the iPad a few thousand times better, so feel free to experiment until the next GM/final build drops next week.