[Huppie]

Could anybody clarify?

You can find quite a bit of information about it here: http://www.engadget.com/2010/01/29/apple-ipad-the-definitive...

Is it just a regular tablet?

It's an iPhone with a huge screen, on steroids ;-)

What OS does it run?

As far as information like this is available before launch, it will probably run a custom version of the iPhone OS.

Is it free?

As you might understand, the iPad itself isn't free. The software on it is (very) probably propietary.

Can I change it to GNU?

In time, it will probably be possible to run a *nix distribution on the iPad, just as you can run these on playstations, xboxes, wifi routers etc.