Instead of messing with the registry you should just be able to disable QoS Scheduler from within TCP.
In WinXP Pro.
1. Goto your Control Panel.
2. Goto Network and Internet Connections.
3. Goto Network Connections.
If you connect to the internet via a router through a network cable then do the following:
4. Right click LAN Connection and select Properties.
5. Look in the white box and you should see something like the following in the list:
Client for Microsoft Networks.
File and Printer Sharing
QoS Packet Scheduler
Internet Protocol TCP/IP
Select QoS and then click Uninstall.
If you connect to the internet directly then do the above but find your connection icon in the same section.
I can vouch for the firefox tweaks.