JSI Tip 6929. Capabilities of the Internet Gateway Device Discovery and Control Client and of Universal Plug and Play.

Microsoft Knowledge Base Article 821371 contains the following summary:

This article discusses the relationship and differences between the Universal Plug and Play (UPnP) and the Internet Gateway Device Discovery and Control Client capabilities of Windows XP. Internet Gateway Device Discovery and Control Client and UPnP each provide distinct, but complementary, features that permit users to easily control network devices.