Window and Windowless Activex Controls

Hi,

can anyone tell me the main difference between window and windowless Activex controls...?

Please tell me how to host a windowless activex control on a c# windows form application...

what could be the main reason for getting "unable to get the window handle for 'xxx' control. windowless Activex controls are not supported" on windows 7 OS and the VS 2008 SP1 and VS 2005 SP2

Thanks in advance..