If you are planning to upgrade from Windows XP to Vista and have IIS and IISxpress installed on you computer then read on.
Windows XP runs IIS 5.1 and Windows Vista runs IIS 7. When you upgrade from XP to Vista you are really getting an entirely new IIS installation, it's not really an upgrade because its essentially a completely new product (IIS 5.1 uses ISAPI and IIS 7 has a new module architecture).
We therefore recommend that before you upgrade your XP system you uninstall IISxpress, perform the upgrade and then install IISxpress when Vista is installed. If you wish to keep your configuration settings then simply backup the IISxpress.config file in your IISxpress installation directory on XP and then copy it over the existing file on the Vista system (you will need to stop the IISxpress service first).