1. Run Regedit
2. Browse to HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\
3. It gets tricky here, there be a bunch of Folders with letters and numbers under this Key, you need to find the one that is your network adapter. Browse them one at a time and look for the ones with similar settings to your network, such as if you have an IP address or a Gateway manually set. If you are unsure, you could always just try adding the line to all of them.
4. Add a DWORD named TcpAckFrequency This is Case Sensitive. If it is already there, skip to step 5.
5. Set the Value of the DWORD to 1
6. Reboot your PC
If you wish to test your lag, the best way to do it is by casting the Healing spell. Try casting all 5 charges of your healing spell before this fix, then after. I guarantee you'll cast them twice as fast after this fix if you have had lag issues or are living on the east coast.
If u have vista it wont work unless u download the hotfix.
http://mattgadient.com/2007/12/13/kb935458-v2-vista-hotfix-for-tcpackfrequency/
Hope this helps ^_^