dear sir/madam:

　　i'm delighted that you have accepted our invitation 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-visual equipment you'll need. if you could let me know your specific requirements by [date], i'll have plenty of time to make sure that the hotel provides you with what you need.

　　thank you again for agreeing to speak. i look forward to hearing from you.

　　sincerely yours,