I don't think a regular blender will work, unless you add quite a bit of oil to keep it softer. A high-powered blender (like a Vitamix or Blendtec) would give the smoothest consistency.
Other nuts are actually more nutritious than peanuts (which often have aflatoxin, a carcinogen, in them). You can make butters out of almonds, brazil nuts, pecans, walnuts, sunflower seeds, or any other nuts or seeds.
If you already have a Champion or Green Star juicer (no use getting one just for this) you can run nuts through it with a 'blank' screen in place and it will grind them into a smooth butter.