I agree with Kurt. Sound is very important. Hooking up your camera to the sound sysem where the microphones are that the speakers are using will provide you with a crisp audio track that also has the right levels, which will allow you to pick up everything that is being said, even if the speaker is talking in a low voice. If this is a paid job, it may also help to bring along an additional cameraman for b-roll shots if you plan on editing the piece as well (even if it's only adding graphics). This will give you something else to choose from if you want to add different angles or keep a certain lecture more interesting for the end viewer of the video.