Hi bobpilot. Thanks for the nice comments. I'm currently in Germany so I don't have access to what I did exactly to straighten the chateau but, from memory.... I used a combination of the the Crop Tool in Perspective mode and one of the Distortion Tools, but I can't remember its exact name... this is in Photoshop.
Hope that helps. I can give you more details when I'm back in the UK in a few days. Derek