Quick Question; Need to add something in first post only

[shibby2]

Hey guys, can someone help me with this?

I'm looking to add an ad in the FIRST post only (of every page) in postbit. I want it to be right below and to the left of the first post's message. I also want it to show ONLY to guests.

I know there are mods out there for this, but every one Ive seen, doesnt seem to do exactly what I want.

Can anyone tell me where/what I would need to edit to make this happen?

I was able to add it in the proper place, but it showed in every post instead of just the first post.

Thanks!