Place a 160x600 banner ad at the beginning in the showthread template

[Pulsorock]

Hello,
I want to place a 160x600 banner on the showthread template. I want it to show it at the same place the first post of the thread starts. This way moving left only those firsts posts and not all the posts below. I photoshoped an example for make a little more clear what I?m looking for. Hope it helps.

Thanks

PS. Thanks for the moderator who move the thread to the correct forum.