Dear sir/madam:
I'm delighted 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,
[name]
[title]