The German computer mag c't has an article in number 1/2007 (Plagiatfinder: Prüfzwang für Studienarbeiten, S. 78) about software for "finding" plagiarisms. Oh well, at least I am correctly sited: It is useless to try and solve social problems with software.
But the article is still quite euphoric about using software. Sigh. My tests in 2004 were not encouraging - often, you could just flip a coin an be just as right about whether a paper was plagiarized or not. But many companies scream now "We are NEW! We are IMPROVED!", so I am forced to spend my summer term's research allowance (all of 4 hours a week out of 18 off teaching to do research) in order to repeat the tests. Stay tuned for the results after the summer break 2007.
Until then: just use a search machine and your brain. You will get better results.