Guys - thanks for cajoling me through the recovery - success at last!
I've been trying to update through iTunes since the problem occurred, working my way through the fixes on this and other threads. I also took my iPad to a registered Apple supplier who tried to update from a computer different from mine with an uncorrupted download.That didn't work. My iPad generally sits in a fridge magnet in my kitchen, where it acts an online cookbook, recipe research and archive tool. IT isn't my skill set, and I didn't have any idea what an IPSW file was until mentioned here.
There are a number of fixes for the iPad2/6,1 download crash on this forum. Some have worked for some users, this is the one that finally worked for me.
Assumptions: your iPad2 crashed on downloading 6.1, wouldn't switch off properly and that you kept getting the "connect to iTunes" page, and iTunes then asks you to restore, but gives you a corrupted file message after it has downloaded the new system. I have a Mac mini desktop.
Here's my recipe:
1) Find out which iPad2 you have via this link - there are a number of choices. For Wifi only models like mine, it will either be the older (2,1) or newer (2,4) iPad2
http://www.everymac.com/ultimate-mac-lookup/?search_keywords=A1395
2) You need this info to choose an appropriate IPSW file. An IPSW file contains the specific iPad2, iOS6.1 firmware that you will download to your desktop computer.
Choose the correct IPSW file from this page - the ones for iOS6.1 are at the bottom of the list before the Comments section.
http://osxdaily.com/2010/11/02/download-ipad-firmware-ipsw/
Ctrl click on the appropriate file and, without renaming it, save to your desk top so that you can find it easily.
3) Hold Sleep and Home buttons on your iPad until the screen goes black.
4) With iTunes open on your desktop, plug your iPad in via USB cable
5) iTunes will prompt you with a number of messages to restore your iPad.
When you get the actual Restore button on screen, don't just press return, Alt click it. This will then give you a Finder window. Go to your Desktop - should be an option on the left panel of the Finder window. Choose the IPSW file you downloaded onto your desktop and press OK. It will then start to load the IPSW file to iTunes.
6) In my case, iTunes did all the work from there, downloading the file and updating my iPad. I lost all data and Apps loaded since my last restore on iTunes. Not the end of the world, just a reminder to backup more often.
7) Your iPad will behave as if it's brand new, and take you through a few screens the first time you use it. You will have to put in your home WiFi network password again. That's it.
Grateful if the grownups on this site could have a look at this to see if I've missed anything. Thanks again for all the help on this forum.