There have been claims in various published technical articles and newsgroup postings that Windows XP always reserves 20 percent of the available bandwidth for QoS. These claims are incorrect. The information in the "Clarification about QoS in End Computers That Are Running Windows XP" section of this article correctly describes the behavior of Windows XP systems.
Clarification about QoS in End Computers That Are Running Windows XP
As in Windows 2000, programs can leverage QoS through the QoS application programming interfaces (APIs) in Windows XP. One hundred percent of the network bandwidth is available to be shared by all programs unless a program specifically requests priority bandwidth. This "reserved" bandwidth is still available to other programs unless the requesting program is sending data. By default, programs can reserve up to an aggregate bandwidth of 20 percent of the underlying link speed on each interface on an end computer. If the program that reserved the bandwidth is not sending enough data to utilize it completely, the unused portion of the reserved bandwidth is available for other data flows on the same host.
For more information about the QoS packet scheduler, refer to Windows XP Help. Additional information about Windows 2000 QoS is available in the Windows 2000 technical library.
There really is no need to disable or remove this. You are not going to see any performance drop.