Statistically Awesome Style Sheets with Compass can help you easily generate sprites. Not only that, it will re-generate the images, re-calculate the position and update the CSS every time you update the source images. This post explains the basics and aims to address the most common scenarios when creating sprites.
Traditionally, settings in ASP.Net apps are stored AppSettings area of the app as a key-value store. More complex apps would create specific config sections. The app would then have a static settings wrapper that would read the content from the web.config.