How can I use Lion's "look up" feature without the trackpad?
From this:


  For years, Mac OS X has had a great shortcut for getting a quick definition of a word: Simply hover the cursor over the word, and press the keyboard shortcut Command-Control-D to bring up a little Dictionary popup. This still works in Lion, but it’s now much more fully featured and also has a great new way to access it.


Your looking for Cmd+Ctrl+D

PS: Thanks for asking, it actually made me look and learn something new