Know-How Exchange : E-Marketing

I need recommendations for a wireless, lavaliere mic that will allow our speakers to record their presentations as they do them. I want something that will sync with the powerpoint recording function and works without restricting their movement at all, so wireless usb based would work well. Does anyone have a recommendation for me? We have a speaker presenting next week and would love to have a better way to record than doing it in advance or afterward. Thank you!