Here is how you embed a photobucket thumbnail which links directly to the picture and doesn't open it in a new tab.
First, you grab the 'IMG clickable thumbnail for message board' link from your photobucket album. For example, it may look like this:
[URL=http://s803.photobucket.com/albums/yy311/quickstix/AI%20War%20Report%201/?action=view¤t=aiwar1.jpg][IMG]http://i803.photobucket.com/albums/yy311/quickstix/AI%20War%20Report%201/th_aiwar1.jpg[/IMG][/URL]
Now, to link directly to the picture, you need to remove '?action=view¤t=' from the URL opening tag, so it will look like this:
[URL=http://s803.photobucket.com/albums/yy311/quickstix/AI%20War%20Report%201/aiwar1.jpg][IMG]http://i803.photobucket.com/albums/yy311/quickstix/AI%20War%20Report%201/th_aiwar1.jpg[/IMG][/URL]
Finally, change the URL tags to iurl to stop it from opening in a new window, like this:
[iurl=http://s803.photobucket.com/albums/yy311/quickstix/AI%20War%20Report%201/aiwar1.jpg][IMG]http://i803.photobucket.com/albums/yy311/quickstix/AI%20War%20Report%201/th_aiwar1.jpg[/IMG][/iurl]
Enjoy.
Edit: Fixed the opening iurl tag in the third codebox.