Slow speed on MacBook Pro connecting to Airport Express

Hi All--

My MacBook Pro is about two years old. Have had no connection issues previously, but now am seeing dramatically reduced speeds when connecting to our AirPort express. Other computers are still connecting at normal speeds for our connection (~18mbps), but can't seem to get anything over about 3mbps now. Haven't changed any settings or anything like that recently. Any ideas as to what I can try?