The Nikon D5000 is adequate for most beginners. The main limitation is that the D5000 lacks AF motor and cannot autofocus some Nikkor lenses. But this is usually not the problem, there are enough compatible lenses with D5000 for most beginners to choose. The D90 does not have this problem, can use all current Nikkor lenses.
Certainly D-SLR will do a very good job of low light and indoor photos, much better than a PS camera. But for commercial advertising, you may want to consider hiring a professional. The professional look of a photo comes from a professional photographer, not just by using a professional camera. It may take a beginner a while to master the manual controls to produce professional quality photos. Indoor lighting can be a little tricky when a combination of lighting is used for decors.
I usually don't take photos of my food, but I got one quick snapshot of my son's birthday cupcakes (before they devour them) to show you the advantage of using a D-SLR versus a PS camera:
I use a Canon D-SLR with flash, this is a close up shot taken indoor with minimal light (they were getting ready for lighting candles). This is an advantage of using D-SLR because you can have a shallow depth of field effect with blurry background, selective focus of what you want to show, and non-direct flash. I use bounce flash with a flash diffuser, to soften the light. This brings out better color of the food (without the reflected light from direct flash of the built-in flash).