Spend your money on good lenses, you'll keep those a lot longer than the camera body. After all DSLRs are now in the digital domain, where innovation runs as fast as it can (and that is fast). In a few years the 300D or D70 will be obsolete, and replaced by a much better model with less noise, more resolution, more image buffers, better TTL, etc etc etc. However, your lenses will still keep their value and will still be usable on the new camera body.
Therefore, decide first what lens family you like better, Canon or Nikon.
Now, if you absolutely need the features of the 10D, for example, then its a different story. If you can do without, go for the 300D or D70.