If you're making an attempt to select a file for upload selenium 2 supports HTML file inputs.
<input type="file" id="upload_here" />
IWebElement element = driver.FindElement(By.Id("upload_here"));
Basically you "type" (with SendKeys) the full file path to the file input element. Selenium handles the file selection dialog for you. However, if you would like to manipulate an arbitrary file selection dialog, you've got to travel outside of selenium.