My vote goes to the FZ20 above the 300D.
With the 300D, you will only have a 55mm maximum zoom, which is not much at all, to be honest..
And lenses for SLRs aren't always cheap..
If, on the other hand, you don't need much zoom and can afford to add lenses/flashes/filters etc, then go for the SLR...
Hope that helps
Chez