Windows XP has IIS 5.1 installed, so use the IIS 5.0 procedure. See this article for an overview of IIS 5.1:
A look at IIS 5.1 in XP Pro - What's different from IIS 5?
IIS 5.1 is a feature only to be found
on Microsoft's XP Pro operating
system. It is not installable
(reliably) on XP Home. Additionally,
there are no plans to update IIS 5.0
on Windows 2000 to IIS 5.1.
IIS 5.1 is basically the same engine
as IIS 5.0 but since XP is a client
operating system, it has the built in
limits that are customary for
Microsoft’s client operating
systems—such as connection limits and
only one Web site. Even though based
on IIS 5, there are significant
differences from IIS 5.0 that you
should know about.
You could also open a page in the browser which runs this simple asp Script:
<%
response.write(Request.ServerVariables("SERVER_SOFTWARE"))
%>
As a side note: it is interesting that IIS (beginning with Windows Server 2000/version 5.0) can't be upgraded without upgrading the operating system. Every Windows version has it's own IIS version:
Windows Server 2000 5.0
Windows XP Professional 5.1
Windows Server 2003 6.0
Windows Vista 7.0
Windows Server 2008 7.0
Windows Server 2008 R2 7.5
Windows 7 7.5
Windows Server 2012 8.0
Windows 8 8.0