testing to see if computer is on

Hi, I have an arduino Duemilanove connected via usb to a computer running windows XP and running on an external power supply to power several servo motors. what I'm trying to do is to detect if the computer is on or not from the USB port. I know I could probably hook up a spare usb port's power to the board's input and read that but I was wondering if there is a quicker non-hardware way to do this. Does this make sense? Thanks

you could send it a string saying "yo im on"

Yeah, I tried that. It doesn’t fix the issue when the program crashes or if the OS crashes/BSOD (but still technically On). Is there a variable or combination of variables or function that tells the board if there is power coming from the USB port or not

I was going to look into that but I thought that USBVCC gets set to 0 if it is running on external power. I didn't test this though. Was my assumption wrong?