I'm glad you found a solution; however, I'd like to make a few comments.
Unless your game is full screen, I'd advise against changing the resolution on your users. This is going to change their desktop resolution which could change the way other applications behave, and at a minimum, could muck up their nice icon placement! :)
Instead, I'd suggest doing one of two things...
1) Update your game to support multiple resolutions. You quite easily detect the screen resolution in C# and if it's beyond a certain threshold, scale up your images and game area.
2) Use a game development platform, either DirectX or XNA. Personally, I'd recommend giving XNA a try actually, it's pretty easy to use and works quite well. You can then make your game full screen and it will use the resolution you tell it. XNA supports this automatically.