I checked on the JPL website, the only ways of detecting extra-solar planets involve optical telescopes (fancy ones connected to computers).
It either studies how the planet moves its parent star via the doppler effect, how the star is moving in comparison to two othe stars that are much further away so they act as stationary points.
Another method involves coplex filters that could allow us to see the light reflected off a planet, or using a physical filter to block out the light of the star, or dectecting slight drops in the magnitude of the star as it passes between us and the star.
You might say that arcebo could dectect some the difference using radio waves, but it might have inaccuracies due to our atmosphere and also, some of those are the types of waves that are either canceled by arceibo or are not in the spectrum range that is being studied. The only way arceibo could discover a planet would be if it recieved signals from a satellite that is designed to studie stars for the possibilities of extra-solar planets.
Also, to DJ-Yoshi, I have found out it is the IAU so dont try and discred me because I made one arbitrary mistake.
If you dont believe me, go here.
http://planetquest.jpl.nasa.gov/news/excitingStep.html
look at the find out more section about how to find a planet.
dont complain that it has kiddy like graphics, the information is still true.