I also can not get Odin to recognize the phone in Download mode. I've been using it for weeks in PdaNet with no problems. I have tried uninstalling pdanet and the drivers, and installing the New PC Studio. It recognizes the phone for file transfer/android modem purposes, but sees it as a "USB Device" fro which it can't find a driver when in download mode.
Windows Vista/7 are not an option as I do not use Windows, and installed it on a partition exclusively for this purpose.