Nikon has a AFS 105mm macro lens... and that is good for macro, esp. if you want to shoot insects as it gives you a greater working distance. When shooting insects, when you come too close, you may scare them away. So, what you can do is to think also what you want to shoot... and if it is insects, get something with a greater working distance... but if you are able to shoot without scaring the insect away, then no problem with 50mm or 60mm lens.
Alot of macro is done manually, which means that you need a tripod... but if you have the AFS 105mm lens, you can autofocus with the D40.
The 50mm 1.8 is a good buy as it is cheap and good (only about $150 2nd hand). You can use the 50mm for other purposes as well... and not for macro... but you can get a +4 close up filter to shoot some macro.
I've tried shooting insects and found that it is not my cup of tea... so I sold away my 60mm macro lens, but bought a close up filter for my 50mm lens... which enables me to come closer to the subject, and that serves me well.
If you are not sure, see if you have friends who could lend you a 50mm lens and if they have a close up filter to try out as well.
What kind of macros do you intend to shoot?