Be sure and use 'green peanuts' with the shell. Those are soft and not previously dried.
I wouldn't even try with dried peanuts, although it can be done with a 24 soak and a longer boiling time.
They can take a long time to boil, even with the green peanuts it's 2-4 hours sometimes, taste and adjust. So, be patient.
For spicy ones--I use Zatarain's crab boil. The liquid version is better for this application than the spice bag (I think it's hotter, I don't like it that much for shrimp tho). You can add other spices too; more Cayenne pepper, garlic, chili powder etc. Don't forget the salt!
Let them cool in the boiling liquid, even overnight if you wish.
I just remembered this: If you don't have access to green peanuts.
Use frozen endamame with the shell on; which should be more accessible in most parts of the US.
Spice them up with the cajun shrimp boil spices, salt; and shorten the temp and boiling (simmering in this case) time about 10 mins or less.
Cool them quickly and keep in the fridge in the liquid for a few hours.
mark, just in case you're not familiar with them, its Edamame (no N) and they are soybeans.
Sam, isn't it true that green peanuts are only available locally to where they're grown and only certain times of year? there was a Chowhound thread about them recently.
Ours (The green peanuts) come from GA and sometimes AL, which is more regional than local. Yes, green peanuts are very seasonal as most of the crop is dried and stored.
I've seen them at the Publix supermarket a couple of weeks ago, it might be a bit early for them. It could be an early harvest, given the warm winter this year. Usually it's spring through the summer.
There just isn't much a demand for them outside of the Southern US. But with shipping and people exploring different foods, it's completely different game in 2012.