The first quesiton you have to ask is "how important are the photographs of the art"? Here are various answers based on your answer to that question:
1) Your answer="Not at all important", return the D3000, get a point and shoot, use the on camera flash, be done for less than $100 and 2 minutes of work.
2) Your answer="mildly important, just to give them an idea of what it looks like", take the D3000 you have, get a 35mm 1.8 lens, set up a few hot lights (CFLs are fine), be done
3) Your answer="Critical. This is reasonably expensive art and they want to know exactly what it looks like", You need three things, a nice Macro/Micro lens (Nikon 60mm is a good choice), an excellent light setup (the above hot lights will kinda sorta work if you put a lot of effort into it), and a tripod. There is NO cheap solution for critical photos, period.
Allan