I think that’s been established already, many times. 
Necroposting is not against the rules, but it is frowned upon (like double posting). As for a good explanation, I refer you to Kaiser.
Originally posted by KaiserVonAlmasy
[b]Necroposting, while not technically against the rules, is widely considered very bad form and poor netiquitte around here. Especially if you’re new. It’s a good way to call down hefty “newbie-hate” upon you.It’s not as bad as spamming or linking to porno sites or making a bunch of posts where you just say “Dark” over and over again like some pokemon from hell, but yeah, Necroposting will earn you a lot of dirty looks…
Generally, if a thread hasn’t seen a new post in a week, or if its dropped to the third page or lower, its pretty much dead and should be left to rest in piece. If it’s only been a day or two and is still on the first or second page, then it’s all right. So always check the “last post” date and time. Kinda like when you’re buying milk and cheese at the grocery store. Check the dates carefully before purchase. [/b]