Note: This following tip will not work on XP Home Edition.
1. Make sure you're logged on as actually "Administrator". Do not log on with any account that just has administrator privileges.
2. Start > Run > type gpedit.msc (not available in home version).
3. Expand the Local Computer Policy branch.
4. Expand the Administrative Templates branch.
5. Expand the Network branch.
6. Highlight the "QoS Packet Scheduler" in left window.
7. In right window double click the "limit reservable bandwidth" setting.
8. On setting tab check the ENABLED item.
9. Where it says "Bandwidth limit %" change it to read 0 (ZERO).
10. Close gpedit.msc.
Effect is immediate on some systems, some need to re-boot.