By default (even with QoS disabled) Windows XP,Windows Vista and Windiws 7 reserves up to 20 percent of your connections bandwidth.
To override this reserve take the following steps.
Make sure you Log on as Administrator, not as a user with Administrator privileges.
1 ) Start > Run > type gpedit.msc
2 ) You will see [Local Computer Policy]
3 ) Expand the [Administrative Templates] branch
4 ) Expand the [Network] branch
5 ) Highlight [QoS Packet Scheduler]
6 ) Double-click [Limit Reservable Bandwidth]
7 ) Check [Enabled]
8 ) Change [Bandwidth limit %] to 0 %
9 ) Click [Apply] [OK]
10 ) Restart
