I'm having a hell of a time getting ADB to see my Nook Color as well. I've tried about everything I know to do.
Running Ubuntu 10.04 trying to connect to the Honeycomb v4 preview ROM. I'm pretty conformable moving around Linux and a command terminal. I can connect to my Evo just fine. I've verified that debug mode is checked on the device, etc.
in w7 64 bit what worked for me was to make sure usb debugging was checked on NC and then uninstall both entries under portable devices in device manager, then install the easy adb package then scan for changes in device manager. and it didn't stick after the first time, had to run the process above last night to make adb see my device again.