I glanced down at my network rate monitor, and my computer is happily doing 100-500KB/s of traffic. Somewhere. But where? From which process? This is Windows XP. I've Googled around, and it's not at all obvious what the right tool is. Task Manager will tell you how much CPU your processes are using, but not how much network bandwidth. The closest you can get is "I/O Reads and I/O Writes" (which may or may not have anything to do with the network).

Thoughts?