don't use a needle

any material that is harder than what your iPod is made of (ie metal) WILL scratch it... i know GamerGirl said do it very carefully, but all it takes is an accidental slip of the needle and you will regret it...
a slightly dampened wooden cocktail stick would be safer than a needle if you want to try picking very carefully under the edge
you might also try the heat approach with a hairdryer to soften the adhesive... (not too hot though... low heat setting... and don't hold it too close to the screen)