I was searching for a 32 bits version of node.js and notices that the last darwin x86 version is on the
The minimum required OS X version was bumped to 10.7 back in April 26 with 204f3a8a0b, which was incorporated only into node v6.0.0, so it is not possible to build v6.0.0 on OS X 10.6 unless you modify
common.gypi and build it yourself. Even then you're on your own since it is no longer supported.
node v5.x and earlier still support building on OS X 10.5+ without any changes, but you'll still need to build it yourself.