Default frame style include wxRESIZE_BORDER, so you don't want to use the default.
Const wxDEFAULT_FRAME_STYLE:Int = wxSYSTEM_MENU | wxRESIZE_BORDER | wxMINIMIZE_BOX | ..
wxMAXIMIZE_BOX | wxCLOSE_BOX | wxCAPTION | wxCLIP_CHILDREN
Take out what you don't want :-)