It was quite difficult to find a driver, but finally I’ve found it!
It allows your Motorola HT820 blueTooth headset to work with Win 7 X64
driver:
http://www.hwdrivers.com/dl/5/002086/d_nbook/v_Acer/m_Aspire%205741G
Motorola HT820 blueTooth headset quick start manual :
http://www.motorola.com/mdirect/manuals/QG-HT820HdPhns.pdf