If money is tight, get the D90 kit with the Nikon 18-105mm lens. Nikon almost give it away (in the kit) and the quality is excellent for an entry-level lens.

You need a versatile lens going from wideangle (18mm) for backstage through moderate telephoto (55mm) when you are going a shoot one-to-one with a model up to longer telephoto (75mm or longer) for the runway shots.

Don't get the 18-55 kit lens which is too short to do the runway pictures. An 18-200 is even more versatile, well-built but out of your budget.

Going back to my point about doing runway shoots in poor light - the D90 is a better choice than the D5000 IMHO.

- To be sure of getting good results you need a lens that can let in lots of light (wide maximum aperture - f2.8 or less) so that you can set a fast shutter speed (1/250 or 1/500).
- Most versatile solution is a pro telezoom (70-200 f2.8 or 80-200 f2.8). However they very expensive and big
- A fixed focal length lens is much cheaper (especially second-hand) and has an even wider aperture.

When I know light is going to be low I take along my 35mm f1.8, 50mm f1.8 and 85mm f1.8. I fit the lens that gives me the right view of the subject at one particular spot (runway choreography is predictable) and just do my images when the model is at that point (going pause-pose-pout). The D5000 won't autofocus with older lenses (my 50mm and 85mm) whereas the D90 will.