The Patriots were found guilty of videotaping an opposing teams sideline with a camera that was positioned near the end of the field. As it turns out, videotaping from the middle of that field was (and probably still is) legal. From the tapes, the camera was recording the defensive coordinator while a call was being made. Any information from the tapes was not found to be used during a game. None of the games that were videotaped were found to be during the post-season. This story broke after the first Jets game of the 2007 season after Eric Mangini complained to the league about it.
The morning of the Super Bowl with the Giants following the 2007 regular season, an article in the Boston Herald reported that a former video assistant claimed to have been involved in taping a walk-through practice of the Rams immediately before the 2001 Super Bowl. This former assistant had been fired by the Patriots. He never produced any evidence other than his recollections. No other news agency reported a primary account of the incident, just re-reporting of the Herald's story. The Boston Herald later retracted it's story. No other evidence to corroborate the former video assistant's story has ever been produced.
So the Patriots were guilty of videotaping an opposing team's sideline from the end zone instead of their own sideline, most likely so that they could steal defensive signals during later games. Honestly, how big of an advantage do you think they got from that? At the time defensive coordinators had big menu-like playcards that they held over they mouths when the made the call. I'd say that the eye poke that Brady got from one of the Ravens defensive lineman last week (right in front of two officials) was worth more than all of those videotapes.