If you use Windows, you should get the Google Pinyin IME:

http://www.google.com/intl/zh-CN/ime/pinyin/index.html

Should be shift+space to switch between English and Chinese input modes. There's also a built-in IME here on Popup Chinese right above the comment boxes in the lesson discussions (but not forum, you guys should fix that!). Just click the "en" box above the comment area.