[Quarkboy]

There is almost no relationship between Japanese and Chinese as SPOKEN language, at least structurally.

Originally they were completely separate, the sentence verb placement is totally different, too.
However Japan never developed its own writing system and with the introduction of the chinese writing system Japan basically borrowed (i.e. stole) chinese characters and applied them to their own language.

The earliest "Japanese" in written form is basically ancient chinese except written in a Japanese grammar, so it's all out of order if you try and read it as normal chinese.
In order to write something down you basically had to know the Chinese word equivalents to what you were trying to say, so that the written language was mostly chinese...
This basically persisted as the writing style, and as readings changed for kanji in china and got re-imported into Japan again, the written language evolved a bit, especially with the spread of Zen Buddhism.

However it was still very difficult to write native Japanese words down. Normally if you wanted to write some native japanese word you would either translate it to a chinese equivalent, or you would write chinese characters that sounded kind of like the original word and ignore the original chinese meaning. However at some point this second method developed its own special characters, as simplifications of common chinese kanji used to represent sounds. This became the hiragana. Now finally Japanese had it's own purely phonetic alphabet, and words that were native Japanese could be easily written down.
That's how we have the hybrid writing system that there is today.

So while Kanji did originally come from chinese, and many japanese words that are written with 2 or more kanji originally come from ancient Chinese, the similarities end there.

For someone who knows no Japanese or chinese, it can definitely seem like the languages are related since they use many of the same characters, but it's like using the same type of paint to paint two different pictures.