Forum Adsense Conditionals for First Post (depending on forum)

[محروم.كوم]

I was wondering if this possible. I would like place a purchased ad in the first of one forum in the first post, but in all other forums using google adsense. How would I do this with conditionals? I remember there being a link to a big post regarding conditionals for the old vb, is there one for 4.0? __DEFINE_LIKE_SHARE__