If someone knows a software with these features:

• Works from the tray area
• Very lightweight
• Works also in Windows XP (preferably workstation, nothing serverish required)
• Can show a bandwidth usage graph, where I can easily see each PC's usage
• I can inspect a computer's connections, find out the ports and applications that are using them (eg, all bandwidth is consumed by PC #3, that's running uTorrent.exe from port 33003)

...I'd happily check it out. I'm only sharing my connection with (at most) 4 computers, I'd prefer not having to add hardware or reinstall my system. Thanks in advance!