void *p in Dialog Class

Hi there,
Can someone please whether it is possible to define a "void" pointer pointing to a dialog class.
I have the followings:-

class MyDialog
{
--------------
---------------
};

This class was related to a modal dialog I created;

In my source code,
----------------------------------------
MyDialog *md;
void *p;

void main(void)
{
p = md;
p->DoModal();
----------------
---------------
}

During compilation, error was "left of ->DoModal must point to Class/Struct/Union". But p is pointing to MyDialog. Whats wrong ??