OK here we go...
1. Go to your photobucket site and look at the picture you want.
2. Click on the IMG tag (see picture)

3. NOW... very important you need to "copy" that tag..
easiest way.. click/hold the control key and the "c" key at the same time.. that is a short cut for "copy" command.
.....
Pasting..
1. Open Chi people reply or new message box...
2. Put cursor in message area like you'd start to write..
3. NOW you will paste the link...
easiest way again... click/hold the control key and the "v" key at the same time.. that is the short cut to "paste" command
(see pic below)
Preveiw your post to make sure it worked. if you need to resize maybe someone else can give instructions. Basically you click on the "edit" button and choose resize.. I'd do 25% or 50% then check it. Also even though it says once you resize you can't change.. you can always delete the picture and upload it again. When you resize it doesn't change the picture file you have on your hard drive only the information that is stored in photobucket so you can safely try the settings.