This is a pretty cool tool, from the Windows Live folks, called Windows Live Translator. You give it a URL, and it takes care of translation from English to Arabic, Chinese, Dutch, French, German, Italian, Japanese, Korean, and many more, and from various of these languages back to English.
The translator provides several options for viewing the original and translated pages, including side-by-side, top and bottom, and hover view, which allows you to view either the original page full screen, with translation provided when you hover over various sections (as shown above), or view the translated page full screen, with the original provided when you hover.
The translation is powered by a project from Microsoft Research, and as I understand it uses examples of translations done by people to algorithmically derive more accurate translations of web pages than traditional computer translations. While it's still not going to be as accurate as having a person translate, it's an improvement, and faster than any person could do the job.
You can also add the Windows Live Translator to your site by simply adding the script found here to your page.