They could probably take some macro shots if you got some close-up filters. The best lenses for macro are fixed, meaning no zoom. The fixed (prime or macro) are much sharper then zoom lenses because all the glass inside is stationary, and does not slide around. Your kit lenses are basically the bottom of the barrel from Nikon, nothing wrong with that since you have to start somewhere. What happens with the macro lenses is they can take pictures much closer to the subject, and usually have a 1:1 output ratio. This means that what you are taking of close up is kind of like laying the subject directly onto the sensor. So all in all, you can take macro shots with your current lenses but will need close up filters to get you closer to the subject. The filters do further distort the picture (beyond what your zoom lenses already do) so it will be tough to get real nice macro shots like you see some of the others posting up.
The other thing that those guys are doing is post picture processing, this is time consuming and can be expensive to get into, but all in all it is worth the time invested. Once you get the hang of it, that goes a lot faster.