Microsoft released a new version of IIS called IIS Express 7.5. It allows you to run a scaled down version of IIS 7.5 on Windows XP and greater. For example, IIS 5.1 ships with Windows XP Pro, but not Windows XP Home. Yet you can still run IIS 7.5 on Windows XP Home. However, please note their may be some features that do work in earlier version of Windows due the changes in architecture.
IIS Express 7.5 does not run as a service and does not require administrative privileges to run. The short term goal was to make it work with WebMatrix, but the long term plans are to replace the ASP.Net development web server (i.e. Cassini) with this product for use within Visual Studio 2010. If you want to try it out, but you don't want to use WebMatrix, you can try using IIS Express 7.5 in Visual Studio 2010 RTM with some effort or you can download the beta of Service Pack 1 for Visual Studio. The product can also be used without Visual Studio or WebMatrix, but You must have the .Net framework 4.0 installed prior to installing IIS Express 7.5.
If you plan to use Visual Studio 2010 RTM, then I recommend creating a shortcut to "C:\Program Files\IIS Express\iisexpress.exe" or "C:\Program Files (x86)\IIS Express\iisexpress" if you are running a 64-bit edition of Windows. Once you establish your site information (see these instructions) you can make changes to the shortcut to align with your project in Visual Studio 2010.