'From Kalamazoo to Timbuktu' written by Harriet Ziefert, illustrated by Gustaf Miller. Synopsis, from allbookstores.com: 'When Mike and Millie get bored and decide to travel from Kalamazoo, Michigan, to Timbuktoo, they must continuously change modes of transportation as their bicycle breaks down, a canoe tips over, and the whale gets tired out.'
allbookstores.com reckon it's just been republished, though amazon.com say it's not due out until June 2003. You should be able to pick up a secondhand copy somewhere on the web...