Like I said your talking about vbulletin not photopost. Photopost is the application installed in say your gallery directory. Your talking about how you can modify your vbulletin posting interface to add some new functionality. That is called a hack or mod.
I linked you to the posting which had the link to the popup which works with vb
3 series. Here is the link to vb
4 series. These mods are not made by us and are not supported by us.
Use them at your own risk. Cel Photo Popup - Insert pictures from vB Albums, Attachs, Photopost, vBGallery - vBulletin.org Forum