Rez your item to be a vendor, make sure it has a place to show an ad if it is not the ietms itself .
NOTE dont sell things with animations texture change scripting et al this way as themselves.
RT Click Edit the item and go to the contents tab
Drag the script and the script into contents
click accept on the pop up
drag an ad image to the correct face
rt click item for menu and choose admin
caspervend website opens you may have to log in and follow same insructions as a single vendor to add item.