Disabling USB Ports on Windows XP

Hi!

As you know, for every USB port on your main board, you'll have two nodes in Device Manager:
1-USB Root Hub
2-USB Universal Serial Host Controller (According to your main board), in my situation, it is VIA

http://img174.imageshack.us/img174/3517/usbdevbl0.gif

When I want to disable a port, I simply choose the second one and select "Disable", so the USB Root Hub is automatically deleted.

Anyway, let's suppose that I'm using one of the ports, how will I know it without testing?

I mean I want to disable the free port, not the used one, but without having to disable the working one by accident then having to re-enable it.