I found an interesting and helpful application that enables you to write and edit CSS code and immediately see what it looks like in InternetExplorer and FireFox. With CSSVista, you can check live pages and local HTML files as well. While editing CSS you will see the changes in a split view (see the screenshot below).
The application can be used on Windows XP and Vista only. You can visit CSSVista home page here or download the installation package directly from here (MSI package, 9MB)