Dear sir/madam:
I'm delighted you hae accepted our initation to speak at the conference in [city] on [date].
As we agreed, you'll be speaking on the topic from [time] to [time]. there will be an additional minutes for questions.
Would you please tell me what kind of audio-isual equipment you'll need. if you could let me know your specific requirements by [date], i'll hae plenty of time to make sure that the hotel proides you with what you need.
Thank you again for agreeing to speak. i look forward to hearin