The biggest worry with a probe to look for life under Europa's ice would be trying to prevent cross-contamination by Earth microbes that may hitch a ride of the probe - we just don't have a way yet to sterilize every single component with a 100% guarantee it will be absoulutly free of *anything* potentially living.
(Preventing potential cross-contamination of the Jovian moons by Earth-life is a real concern for NASA - it's a major reason they decided to crash Galileo into Jupiter: http://www.cbsnews.com/stories/2003/...in574222.shtml
It's the same problem that has kept scientists from probing lake Vostok on Earth yet, even though - much like Europe - we really think there could be life in the water under the ice. ( http://news.nationalgeographic.com/n...tic_lakes.html
We just don't have the technology yet to ensure that absolutely *nothing* from Earth isn't hitchhiking on a probe - life's just too damn tenacious, it just somehow always...finds a way.