Since you said it was a forum.. how on earth did you get people to post to it when started from zero posts ?
Congrats, those are great numbers. I'd also like to know that if possible. Edited: Nevermind, I found your answer here
Google is your best friend anyhow, vbseo is a vbulletin plugin that allows you to do SEO on your forum. www.vbseo.com
Seriously, if you have a forum, you don't even need vbseo or any other plugin, just need good old content. I was brainwashed into buying vbseo but it's not that bad, it does good things to the forum, nicer urls easier to remember, could of done with zoints but at that time I didn't know about zoints. Anyways, no you don't need a forum to do SEO.
is your site this one: http://www.carsdiscussion.com/ ? There's an administrator by the name M5love there.
what ways did you use to advertise, to get the traffic that you were getting? feel free to PM if want.
this will help people who begin adsense making a idee on how much income they can usually make ! 10 sites like that and its 3k/month ! great work !