You installed IIS 7.5 Express, the full IIS 7.5 only runs on Windows 7 / Windows Server 2008R2.
IIS Express does not have a user interface nor any entries in your start menu. You usually use it from within Visual Studio or Web Matrix.
There are some third party tools that add a UI to it, CodePlex has some.
The files are in:
C:\Program Files\IIS Express
and the configuration for your sites is stored in:
On XP this path looks a bit different