Note: I have no idea what this fix will do to your torrenting, but I haven't noticed any negative effects so far. This fix is also for XP only - Vista and Windows 7 users are on their own, just do a search for TCP ACK Frequency and you should find the answer.
Open your registry editor (Start > Run > regedit).
Open your HKEY_LocalMachine\System\Current ControlSet\Services\Tcpip\Interfaces
You then need to find the interface that has all your IP address settings. Once you find the right interface, create a new Dword Value called "TcpAckFrequency" (caps are important, skip the ""). Set the value to a Decimal 1, and reboot your machine.
You should see a great reduction in your ping time at this point. Note, you should always backup your registry before you try editing it, and if you don't know what you're doing - I'd avoid it all together.
Note: The one drawback I've found is that I'm actually suffering from playing 'too fast'. I'm used to playing at 1/4 sec lag, so things seem really fast. It's awesome!
It didn't make me an instant God in Arenas though - still working on that hack.