If they are specifying OS for the drive, it may have its own driver. The driver may require OS w2k or newer. If it didn't have a driver, I couldn't see them caring. Sometimes you can get cheap hardware to work on a box by doing some translation or such in a filter driver.
On the other paw, they could have only tested it on w2k and xp so that's all they put on the box. Only one way to find out...