Determines the percentage of connection bandwidth that the system can reserve. This value limits the combined bandwidth reservations of all programs running on the system. If you enable the setting, you can use the "Bandwidth limit" box to adjust the amount of bandwidth the system can reserve. If you disable this setting or do not configure it, the system uses the default value of 20 percent of the connection.
But If a bandwidth limit is set for a particular network adapter in the registry, this setting is ignored when configuring that network adapter.
Here step by step to TUNE UP your bandwith limit in Windows XP > Group policy :
1. Go to "RUN" and type : gpedit.msc
3. Double Click > "Limit Reservable Bandwith"
4. Limit Reservable Bandwith > Enabled , Bandwith limit 20% change to > 0%
5. click OK, and Restart your connection.