Is there an easy way to detect different browsers. Or atleast a way to change an id padding in css for firefox. In my aspx pages I change the css filename, but my code still uses the old css file. Is there something I need to do in order for the new css file to be used?

Yes, if what you need to do is to have some corrective CSS, there is the possibility of adding specific CSS depending on the browser. This is the quick and easy version.

Look at the Dark Knight skin for example and you will see an ie7skin.css file. Look at the skin files and you will see how this is called.

You can get a bit better control over these things by using the 40Fingers Style Helper Skin Object in your skins. You can read more at http://www.40fingers.net/.

I like using the Style Helper to load additional CSS files to correct little browser issues.

DotNetNuke 6.1 introduces Client Resources Management which is a new, improved, and very powerful way of dealing with these issues. I hope we will have a tutorial on that one of these days.