Get user approval before taking control, for each connection

[דוד גדעוני]

Hi everyone, 

When I take control on a Win98/2000/NT PC using the VNC, I want that the
user will give me his approval to do so, for each connection.

I am a new user in VNC and I read the documentation carefully.  I didn't see
any details about such an option.

Does any one know if it's possible to do with VNC ?  If not, can you
recommend on another freeware/shareware application with such option in
Windows 98 & 2000/NT environment ?

Thanks a lot for your help, 

David.