Creating file in asp.net and saving it on server?

Hi
I have made some code that creates a file for later use. The file just needs to me stored at a temporily place on the server. What do I write in my code if I want to save the file in a certain folder on the server? The file shoul dnot be save among the aspx files and the other web site content but in a folder that not should be accesiably from other than the website.