I just realized that I have a process inetinfo.exe always running on my PC. It seems to be part of IIS. Even if I kill it, it starts again with obviously a different port id.
How can I see in Windows XP which application triggers this process to start?
There is a tool Process Explorer that can help you to explore all the process and the resource used....
Inetinfo.exe (IIS 6.0)
When IIS 6.0 runs in worker process isolation mode,Inetinfo.exe is a user-mode component that hosts the IIS metabase and that also hosts the non-Web services of IIS 6.0, including the FTP service, the SMTP service, and the NNTP service.
Inetinfo.exe depends on IIS Admin service to host the metabase. When IIS 6.0 runs in IIS 5.0 isolation mode, Inetinfo.exe functions much as it did in IIS 5.0. In IIS 5.0 isolation mode, however, Inetinfo.exe hosts the worker process, which runs ISAPI filters, Low-isolation ISAPI extensions, and other Web applications.
In IIS6.0, regardless of the application isolation mode used, the services that run in Inetinfo.exe run as dynamic-link libraries (DLLs) under the Local System account. Because a Local System account allows users access to every resource on the local computer, use caution when you run services in Inetinfo.exe, especially on computers that provide services on the Internet.
From MSDN InetInfo