On the page of where your desired photos are shown as thumbnails, underneath the photos you should see this:
"Url [link]"
"Tag [link]"
"Img [link]"
Where it says "Img" highlight the link beside of it, right click where its highlighted, and click "copy." Come back to the reply or new topic screen, right click and choose "paste." Another way of doing it is highlighting the link, pressing ctrl c, then pressing ctrl v in the reply or new topic screen.
After you click paste (or press Ctrl V), a link shows up similar to this *without* the spaces:
[ IMG ]http://img.photobucket.com/albums/v627/Username/photoname[ /IMG ]
Do this to all the photos you want to post, click preview post to make sure everything is coming up ok, and then you're done.
Example: