you don't need a macro lens, it helps, u can use close up kits, teleconverters or extension tubes to increase magnification, but macro lenses tend to yield the best quality i have a close equivelant to the d40, the d50, one main difference is that the auto focuses of many lenses don't work on the d40 or d40x,
macro is a pretty relative term these days and you can take 'macro' with a lot of lens
true macro lenses are ones that make a 1:1 magnification ratio and are prime lenses, there are quite a few zoom lenses with a macro feature, but it doesn't give the same magnification, things to consider
i have the tamron 90mm macro lens and am happy with it, i believe there is still a $90 rebate on it putting it around $400
