Well, I had a D30 and quickly replaced it with a D60 - although essentially the same camera in many respects, as well as the large sensor Canon made a number of improvements to the software. While it does use basically the same AF
system, the accuracy and responsiveness was much improved (though they didn't really get this right until the 20D) and file writing/buffering were enhanced. Net result is that the D60 is a more effective camera.
However, these cameras are over 2 years old, and the shutter is rated at 30K actuations. Many of the used examples will have exceeded that (doesn't mean the shutter is about to fail ... but it might). I would think that a new 300D would run cheaper than the cost of a D30/D60 plus a shutter replacement within, say 12 months.
But if you can source a used D60 which has been lightly used (be careful, the frame count accessible by the user can be reset!) it could be a very good buy.
Colin K. Work, Pixstel