In windows xp 20% of connection bandwidth is reserved, this is reserved by QOS(Quality of service) scheduler . So you can increase your bandwidth by up to 20%, if you disable this reserved system bandwidth.

How to do that ?

• Open run prompt (windows key+ r)


• Now type gpedit.msc and the group policy editor window will appear.
  


• Then expand the directory to the following setting

Local Computer Policy ---->Computer Configuration ---->Administrative Templates --->Network ---->QOS Packet Scheduler

• Now you can choose either of the view standard or extended (it provides explanation of the property you select)


• Now right click on Limit Reservable Bandwidth and choose properties (as shown in following figure)

























• Now select enabled radio button and set bandwidth limit to 0% and press ok.