It appears that Windows XP's Quality of Service function reserves upto 20% of the available bandwidth, even when disabled in the network settings. Following these simple steps will restore the full bandwidth to all network connections.

Make sure your logged on as actually "Administrator" (not an account that just has administrator privileges).
Start - run - type gpedit.msc
Expand the "Computer configuration" branch
Expand the "Administrative templates" branch
Expand the "Network" branch
Highlight the "QoS Packet Scheduler" in left window
In right window double click the "limit reservable bandwidth" setting
On setting tab check the "enabled" item
Where it says "Bandwidth limit %" change it to read 0-- Click apply, OK, exit gpedit.msc
Go to your Network connections (start->my computer->my network connection-> view network connections). Right click on your connection, choose properties then under the General or the Networking tab (where it lists your protocols) make sure QoS packet scheduler is enabled.
Reboot , now you are all done.


from http://www.zensupport.co.uk/ADSL/USB....asp?URL=winxp

Damn the search facility on here - we had this topic a couple of months back. Its does work but not that much difference

www.tweakxp.com