The galleries are not supposed to be used to post pictures in the forums. You only have a certain ammount of slots (so you will have to delete them frequentelly and that means that the links will not work for long and they also take a huge chunk of space on the server).
It's best if you use storage sites like photobucket or imageshack. They are reliable, totally free, allow you to organize albums and give you the code you need to post pictures in different kinds of forums and blogs. Some also allow you to resize pictures and use thumbnails.
Check this thread for an example.
http://www.one-ring.co.uk/phpBB2/viewtopic.php?t=13053