This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
You can use the frame as the first parameter, or any control (component) you put into that frame. The only difference will be how the dialog will be placed on the screen; it will be centered around the component. If the frame is the first parameter than the dialog will be shown exactly in the center of your frame. If it's a button in your frame it will be centered around the button. In both cases it will block access to the frame.