If you have downloaded Pro Tools LE 7.3 or installed it by any means other than the DVDs that come with the unit, then the 003 will not be recognized. This is because 7.3 was released before the 003, and the default installer doesn't install the proper drivers and controller personality.

To fix this issue, there are two options:
1) Install Pro Tools LE 7.3 from the DVD that came with the 003, or
2) Install the Pro Tools LE 7.3.1 and 7.3.1cs2 (or higher) updates - this should contain all the proper files for the 003.

For the most current Pro Tools CS Updates, see the Pro Tools CS Updates page under Quick Links in the Support section of Digidesign.com