Why cant i view usb directory in DOS windows 7

Greetings,
I'm trying to create a portable Ubuntu machine on a USB drive. Unzip/installation instructions I have require command line inputs to do this. I'm sortof a NEWB when it comes to DOS but am pretty familiar with Linux command line - at any rate I don't know how to change directory in DOS to view the USB directory.
Stuff I've tried ("J" is the drive of my USB):
cd c:\
cd c:\Windows (and users)
cd J:\
CHDIR J:\
CHDIR J:

Help?

Thanks muchly =)