I'm using BWmeter on WinXP. It's not bad, and can be configured to monitor ports, and protocols (or not, if you prefer). There is time-limited demo at www.desksoft.com
Mine expires tomorrow, will have to decide whether I'm prepared to pay to continue to use it.
Only problem that I have is that if the time interval is set too low (i.e 1 second), then it returns some funny spikes, if the interval is set to 2 seconds then it's fine.
MW128, Tower <b>60</b>(Northpark Plaza), Signal:16%,S-N-L: 7, BER: 45%