Changing the visibility property of one form from another

Question

Hi,

I have an windows form....where i m doing authentication.

When a user clicks a button I am showing a login form where i am doing the authentication. If the user is authenticate I need to make the panel visible which the user has clicked before authentication in the main form.

How can I change the property of a form from another form.

If anyone has some idea...do help me...

thanks in advance...