What lenses do you have? Unlike the D50, the D5000 does not have a built in focus motor, so will not AF lenses with screw drive focus.
Apart from that, it will be a good upgrade. Also consider a S/H D90 which does have a built in focus motor and the same sensor as the D5000, but more buttons and two control dials. I went from a D50 to a D90 and IMO it was worthwhile
I don't think d50 to d5000 is much of an upgrade to be honest. As suggested a d90 would be they way I would go.
