Hello,
First you need to look in the settings table of photopost not vbulletin.
Ok I made screenshots of the steps... tell me if you did follow me
http://valve.be/movies/pinpoint.swf
As you have 4.8.6, if you don't find id 172, that means that something wrong happened during the last upgrade.
I think i saw a thread of Omegatron or Michael telling that there will be a field for the cookie in the admin area settings, it will be for the next version.
If it's not possible to get it working, you can buy a installation script or upgrade package from photopost.
Later,
Interdit