Hey, jimbobuk, this hasn't been covered here for a while, so here's the short version. (if you want the long version you'll have to run a search for it

)
This is from the beginning, so forgive me if I cover stuff you've already done.
When you install the Connect software, it ought to ask you if you're in the U.S., just tick the box (otherwise it won't let you do the install).
Once it's installed, when you're connected to the internet, run the Connect Reader software, and click on the "eBook Store" selection in the left column. It'll think about it for a minute, then take you to the store.
Once you're there, click on the "Register" or "Log In" link in the upper right corner. You'll get prompted to create an an account, go through the steps, I don't remember them, I'm afraid.
Once you're logged in you might need to go to the Account link in the upper right again, and choose "Manage Devices" from the middle, left column in the lower right window. You'll need to register your PC, and hook up your Reader to a USB port, and register that.
That should be enough to get you your credit. You should be able to see it in your account's Transaction History (lower right option on the Account page), and you should get an e-mail pretty quick besides.
That's it, just use it before the end of January or it turns back into a pumpkin.