In photobucket, there is a link which is titled "direct link" under your photo (in the thumbnail section) or to the right (in the edit section). You first copy that (highlight and then press control+C or right click and choose copy).
Then when you go to the advanced posting on B&B there is an icon above the text box that is a yellow box with some pyramids and a little square (if you hover your mouse over it, it says "Insert Image"). Click that button and then paste your link into it (control+V or right click and choose paste).
That should post the picture for you.
(I tried to make it as simple as I could as I don't know how computer savvy you are.. so sorry if it sounded l was dumbing it down too much or anything.. and if it is still too hard, tell me and I'll try and make it even easier)