I'm searching for a PC software that to send commands through a USB port.
> Does anyone know about one ?
I'm assuming you mean, "from user mode?" If you only want to talk to HID devices, in Windows XP and above you don't need any software -- it's built into the OS. For arbitrary devices and commands, I've used DriverX USB in the past, but it's not free. I believe there are some open-source packages out there that do roughly the same thing, however -- I'm certain there are for Linux, if that'll work for you.
I also seem to recall that supposedly in Vista there were going to open up USB more completely in user mode, but I could just be making that up.
---Joel