We were set an algorithm problem in class today, as a \"if you figure out a solution you don\'t have to do this subject\". SO of course, we all thought we will give it a go.
Yeah I'd go for the wordnet approach.
Check this tutorial on WordNet-based semantic similarity measurement. You can query Wordnet online at princeton.edu (google it) so it should be relatively easy to code a solution for your problem.
Hope this helps,