We (the community, in a long discussion on the Community board) came up with an intellectual property policy a few months ago. You can find it in the User's Guide. In "Some Rules to Live By" there, I stated the Zone's position on who owns material posted here:

Who owns the copyright on material you publish here? Unlike some discussion sites, we don't greedily assert that we own what you write. Instead: You retain the copyright to what you write. By publishing it here, you automatically grant to HabitableZone.com an irrevocable license, in perpetuity, to publish your work on the Internet, in a compilation we build out of your messages and the messages of others; and to distribute the compiled work in other media in the future. You agree that the HabitableZone.com is a "common carrier" which is not responsible for the content of your published work, and you agree to defend and hold harmless the HabitableZone in the event of legal action as a result of something you wrote.

So, your instincts are correct: You should treat everything posted here as if it belongs to the poster, and get permission before reproducing it elsewhere.