SO you have a prebuilt/store bought NAS? Hmmm, I've always heard bad things about those because they are geared towards Win/Mac boxs.
If you haven't had it long, I'd suggest taking it back and picking up an old P-III and installing FreeNAS (google it). I have had NO problems getting onto it with Mac, Windows, and Amiga. It's alot more configurable then the commercial products you can get...