If anyone is having trouble with adb not seeing your N8x0 on Windows XP, I have found a solution. The usb driver that comes with the SDK is only configured for the G1 and the HTC Touch. It does not have the vendor (VID) and product (PID) numbers for the the N8x0 port in the android_usb.inf file.

Using the Microsoft USBView - USB Connection Viewer from http://www.ftdichip.com/Resources/Utilities.htm I determined the PID needed to be 0001.

With this value added to android_usb.inf, the driver installed on Windows XP and running "adb devices" listed my N800.

I've attached a zip of my modified android_usb.inf, If it doesn't work for you try using USBView to check your VID and PID numbers.