umm..how long does it have to be before a thread is deemed unpostable? is it like 6 months or 9? or when someone feels like closing it?xD

From the Basic Site/Forum Rules sticky: "Do NOT necro old topics. If a topic has not been posted on in three months, is a topic about something that is no longer in function or no longer applies to anything on-site, do not revive the topic."

Exceptions: "The following forum boards are an exception to this rule:

• Suggestions & Ideas (including its subforums) - Do not bump or otherwise revive threads that have not been posted on for 15 months or more.
• Problems & Bugs (including its subforums) - Has no necro rule.
• Site Feedback (including its subforum) - Has no necro rule."

thanks! "do not revive the topic." ..Does that mean just don't post on it, but you can create a new thread for it?

Yep! Don't post on it (hence the phrase "necro", as in "necromancy", ie, bringing something dead back to life). New topics can be created.