QoS (Quality of Service Packet Scheduler) controls the rate of flow for various network services. It's not really useful unless you're using apps which are QoS-aware or running a server, so you can gain some extra bandwidth back by turning it off.
Simply go to Control Panel -> Network Connections -> Local Area Connection -> Properties -> Uncheck the QoS Packet Scheduler.
If you are using Windows XP Pro, you can modify or disable the QoS using tweaks found at
TweakXP or
Earthlink Support.
As for your audio/video troubles, try having a look through some
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