Dear madam:
I'm delighted you have accepted our invitation to speak at the Conference in on .
As we agreed, you'll be speaking on the topic "" to . 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 , 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 you.
Sincerely yours,