MDI Child Controls Interacting with Parent Controls

Question

G'day everyone,

I'm fairly new to Windows Forms applications in C# so I apologise for what will undoubtably be a trivial question, however I two questions I was hoping someone may be able to help me with
(1) Consider a Window's Application, with a main Form that contains a picture box and another form used as a pseudo OpenFileDialog box with a simple text box and command button, if I add the pseudo OpenFileDialog form as an attribute to the Main form, how am I able to set things up so that when the button is clicked the information is sent to the main form ??
I.e. the user clicks File --> New ( then the pseudo OpenFileDialog is initiated) the user enters the path and clicks the button, which I then want sent back to the Main form to open a picture in the Picture Box in the Main Form
(2) Is it better to do this sort of thing as an MDI and if so how??

Any help would be greatly appreciated,

David