We use the Cisco VPN Client at work, which adds the Deterministic Network Enhancer miniport driver.
Check if you've got a VPN client installed ones which use DNE are Cisco, Safenet, Unity, Borderware...
You should be able to go into TCP/IP properties of the network connection and un-select it. Also try disabling any VPN services you find in cntrl panel --> admin tools --> services.
Sometime VPN clients may give you connection problems to your ISP due to setups etc... however it shouldn't affect performance.
cheers,
Jai