How toenble & disable edit boxes

Hi everyone. Just when you thought it was safe to look at a question. I'm back!

Still doing edit & static controls in dialog boxes.
I would like to display and remove boxes depending on selection in checkbox.
eg. click checkbox and change an edit box from enabled to disabled to enabled etc.

case      IDC_CHECKBOX:
{                        if(1==SendMessage(GetDlgItem(hdlg,IDC_CHECKBOX),BM_GETCHECK,0,0))
{SetWindowLong(
GetDlgItem(hdlg,IDC_TEXTBOX),      // handle of window
GWL_STYLE,      // offset of value to set
ES_RIGHT | WS_BORDER | WS_TABSTOP        // new value
);
                                                MessageBox(hdlg,"Clicked","",MB_OK | MB_ICONINFORMATION);
}
else
{SetWindowLong(
GetDlgItem(hdlg,IDC_TEXTBOX),      // handle of window
GWL_STYLE,      // offset of value to set
ES_RIGHT | WS_BORDER | WS_TABSTOP | WS_DISABLED       // new value
);
MessageBox(hdlg,"UNClicked","",MB_OK | MB_ICONINFORMATION);
}
break;
}

I know that the message is being seen as the correct MessageBox is shown when I click the checkbox. All that happens though is it disables the edit box permanentley.
Like I say, I would really like it to disapear the become visible when I want it to be.
I am sure this must be trivial but I've been trying to do this for three nights now (It is a home project and it's driving me mad)
Regards to U all.
dsch
P.S.
Please no MFC or OWL
The app is win32 written in c++