Setting the screen resolution takes some API calls. There are threads here that have it, do a search for them.
Just as a note, setting someone's screen size through code without their approving it is generally frowned upon. It's better to either:
1: Give them a messagebox that tells them that the screen resolution has to be a certain size before your program will run, and let them decide if they want to do it.
2: Use code to adapt your forms to whatever screen size the user has.
Robert