Mac's Oxford Dictionary

Well I turned of the internet both before and after using it on both 10.5.0 and 10.7.3 on an Intel Mac. Sounds like you have something wrong with your internet setup that is being picked upon by the dictionary application. Are you really running 10.5.4?

Still doesn't explain why it doesn't work. Open Network utility and traceroute www.oed.com That might reveal a network issue.

Also when you say boot off, do you mean the program just closes? Or is there an error it reports?