By Default, XP reserves 20% of your bandwidth for it’s own use. This is
a crying shame and should be undone immediately. To do this, you will
 not require any additional software, just follow the steps below.

1. Access the Group Policy Editor. This can be done by typing gpedit.msc
    in the Run box (Start, and then Run). You will now be looking at
   something like this.

   

2. Navigate to Computer Configuration/Administrative Templates/Network/QOS Packet Scheduler using the pane
    on the left side.

3. In the left pane, there should be a Setting with the name 
   Limit reservable bandwidth, right-click this and select properties.

4. Now this might seem a bit weird, as the State will say "Not Configured”
    but Windows by default will reserve 20%. So the trick is to set it to
    reserve 0%. You can do this by clicking enabled and then
   setting the Bandwidth Limit % to 0. It should look like the image below.

   

5. Hit OK then close the Group Policy Editor.

That’s it! You’re done with the first tweak. Just a quick side note
 here, there are lots of other little things you can change easily
using the policy editor. Feel free to wander around!