iPad 2 is dead after failed upgrade
Make sure the iPad is turned off. Hold Home and plugin the Dock Connector cable. If the iPad shows an attach to iTunes screen, you can restore it. If it doesn't, you have to put it into DFU mode. It's a bit tricky, so don't panic if you doesn't manage it the first time. When you're in DFU mode, iTunes will ask you to restore it.

A tutorial for iPad DFU is this one:
http://www.youtube.com/watch?v=DWy2xG0U4u8
It's looking as if you would have to have a running iPad, but it does work the same way if it's turned off. This is also true for iPods and iPhones.

There is no way to brick your iDevice using software. If you can't get it to work using these two tricks, its hardware is faulty. Good luck!