I am looking for a book that has the Canterbury Tales in the original old English on one side of the page and a 'translation' into modern English on the other. Any ideas?
I don't know about a book, but a Google search on
canterbury tales
produces as its first reference
http://www.librarius.com/cantales.htm
which does just what you ask
The Riverside Chaucer published by the Oxford University Press has the Middle English (not Old English - that's very different) on top and modern English underneath.