If you are using vBulletin, there are some template hooks you can use. Or, Go to ACP > Styles & Templates > Style Manager > Select the "Edit Template from the DropDown Menu > Double Click on Ad Location Templates > Double Click on ad_showthread_firstpost and paste your ad code there. Ads will be shown after the first post. If you are talking about the ads in the first post contents, then you have to ask Shawn. He coded that himself for DP only.
thanks for RE digitech as you say it's not free ... just for Digital Fourms only .. No problems thanks .. am search for this since along time and i can't find it thanks again