Do you ever see yourself or have interest in taking pictures for money?
(If yes look more closely at a body with a FX sized sensor; Serious hobbists and prosumers are happy with the DX).
FX lenses work with DX but there is increased magnification. DX lenses will only focus the image on part of the sensor of an FX camera (should you ever go truely pro) they work, and the camera recognizes them as DX lenses you just don't get to use all of the senor (and in 10mp + cameras it's not so much of a big deal).
The D5000 does unbelieveable stuff. I actually considered one, but I have several lenses from my previous gen Nikon 35mm AFs that won't work with the 5k because it lacks the drive motor for those older ones (legacy AF lenses). I am personally going to have to wait for something to replace the the D90.
The good thing about the d5000 is you will be able to start using without any of the classes, just set everything to automatic and use the presets just like a p&s. It takes fantastic video too.
I would encourage you to look at the two lens bundle or, if you can find it, the 18-200 bundle. The 18-200 lens is one that could carry over for a long time to come. The other two are fine, don't get me wrong- but they don't have that three decade build quality of some of the other lens.
I'm a Nikon guy, but don't rule out Canon because they have great bundles and make fantastic camera bodies.